Print Conductive Circuits With an Inkjet Printer

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Needed

• Inkjet Printer ( Brother MFC-J450DW)
• Silver Nanoparticle Ink
• Refillable Ink Cartridges
• Refill Syringes
• Printer Paper
• Quick Drying Transparencies

Optional

• Electrical Tape
• Copper Tape
• Circuit Components
  
  • LED
  • 330 Ω Resistor
  • ATtiny85
• Dremel
• Power Drill
• Hacksaw

Printed electronics can refer to a wide range of techniques that are used to print electrical devices onto a substrate. A substrate is just the technical term for any substance that the printing process takes place on such as paper, glass, cover slips, etc. The techniques for printing electronics are still largely being developed. Some of the main techniques include screen printing[1], rotogravure[2], and inkjet.

Why use printers at all for electronics? Currently there are two main ways of prototyping a circuit, breadboards and printed circuit boards (PCB). They both have their own pros and cons. A breadboard allows for a cheap way to easily connect wires and different components. However the standard layout of a breadboard means that you must conform your parts to fit what you are given.[3] A PCB can be designed to suit the exact needs of the project you are working on. The manufacturing costs of the PCB are its downfall for hobbyists however. It can take weeks to have your order made and shipped to you or the use of potent chemicals if you wish to etch it yourself.[4] The ability to print electronics on demand combines the best qualities of a breadboard and PCB. They are cheap to print, easy to add parts to, and can be revised very quickly. Printing electronics is becoming to the electronics industry what 3D printing has become to the mechanical industry.

This project will focus on the inkjet printing method for it is the cheapest and easiest method for hobbyists to get started with. Inkjet printers work mainly by one of two ways. The first being a “Thermal Bubble” where a current is first sent through tiny resistors in the print head. These resistors give off heat and vaporize some of the nearby ink. This vaporization of the ink creates a gas bubble which, as it expands, pushes ink out of the nozzle in the form of tiny droplets. When the bubble eventually pops, a vacuum is created in its absence which refills the nozzle with ink.[5]

The second method is known as a “Piezoelectric” printer. Piezoelectricity is a material property where if a mechanical stress is applied, an electric potential is created. The opposite is also true, if a piezoelectric material is exposed to a change in electric potential energy, then its volume will change.[6] Piezoelectric printers utilize this property by having piezoelectric crystals in the print head’s ink reservoir. When a voltage is applied to these crystals they deform and expel tiny ink droplets out of the nozzle. [5]

When selecting a printer, almost any inkjet printer will work. Some researchers claim that it is best to use a piezo-driven printer rather than a thermal-driven one as it is less likely to alter the structure and properties of the conductive ink.[7] It doesn’t need to have fancy touchscreen controls or wireless connectivity. Just look for a cheap printer that you would feel comfortable taking apart and modifying. Studies have shown that Brother Co. printers are the preferred option when it comes to printing circuits due to their nozzles releasing higher volumes of ink. [8] More ink on the page means that there is a better chance of a solid connection or trace being made. This project will use a Brother MFC-J450DW. This model was chosen mostly due to the fact that it was the cheapest on Amazon for about $80 at the time of purchase.

The one downside with this printer is that the cartridges do not contain the print heads themselves. Instead, these cartridges simply act as reservoirs for the ink. The ink gets pumped out of these cartridges and into the print head. The tubes for which the ink is transported (from cartridge to print head) in already come pre-charged with ink. This can make the process of draining the original ink a little more tedious (this process is explained later on).

There are many properties such as viscosity, surface tension, volatility, and particle size that need to be taken into consideration for choosing a suitable ink. Luckily, an extensive amount of research has already been done on this and there is a clear winner. Silver nanoparticle ink, part number NBSIJ-MU01, from Mitsubishi Paper Mill works the best for most applications.[9] This ink can be purchased from Diamond-Jet for $340.00 per 100 ml.[10] Admittedly, this does sound like a daunting price at first. However, most conventional ink cartridges only contain between 10 – 15 ml of ink inside of them. So overall the price per ml isn’t that much more expensive. With a 100 ml of silver nanoparticle ink you will be able to print hundreds of circuits.

Another benefit of the NBSIJ-MU01 ink which helps justify the price is that it is chemically sintered. Sintering is the process which take a powdered material or solution and transform it into a solid. With inkjet printing the printer does not print continuous lines. The printer prints many small drops of ink. The sintering process helps combine the silver nanoparticles in these drops together thus creating a complete circuit. Traditionally, the inks would have to be sintered or “baked” in an oven for a few hours so that the solidification process would take place.[11]Chemically sintered silver nanoparticles are dissolved in a special solvent that allows for the reaction to take place just seconds after it is printed.[8] This dramatically reduces the time it takes to prototype a circuit.

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The first thing you will need to do is install the printer drivers from the provided disk or the manufactures website. Follow the provided prompts and connect the printer when it advises you to.

When first connecting the printer you will need to set it up with the ink cartridges that came with the printer. This really is not that big of a deal considering the tubes are already filled with ink and will need to be drained later anyways. The printer will enter a cleaning process and then prompt you to run a test print when it has finished.

The refillable ink cartridges came with a small plastic lever/hinge. There is a "safety" feature on the printer that does not allow the printer to operate when the print door is open. The printer can be tricked into thinking that the door is closed however by using the lever to press this switch. Simply slide it into the crack and jiggle it around until the "Ink Door Open" error goes away. The refillable ink cartridges will end up protruding from the printer itself (when you later install them) so this is a good thing to get out of the way now.

Alternatively, the door that came with the printer can be modified if using the hinge becomes a burden. This modification was done by using a combination of a hacksaw, drill, and dremel to cut out the majority of the door panel. The door would be able to be closed but there was still room for the ink cartridges. This can be seen in the last pictures above.

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The first thing to do is install the provided air filters on the top of the cartridges. Ink cartridges have this hole so that a vacuum is not formed inside of the container when ink is being drawn out. Normally the cartridges do not need a filter because they are fully enclosed in the printer. However, after disabling the "door open" warning with the provided hinge and having the ink cartridges extend beyond the printer chassis, these are recommended to prevent debris from contaminating your ink.

Next install the provided rubber stoppers. This will be the spot used to fill the cartridges with ink.

There is a thin film covering the back of the ink cartridges. This can be left alone as it will break itself when firmly inserted into the printer.

The printer measures the ink level of the cartridges in two ways; visually and mathematically. For the first reason it is recommended that some black, electrical tape be placed around the small window on the back of the cartridge (shown in the image above). This back window is what the printer looks at to see if there is ink in the cartridges. It would cost a lot of money to completely fill each cartridge with conductive ink so this helps trick the printer into thinking they are full. Each cartridge also comes with a small chip on the top of it. If the printer ever tells you that you are running low on ink (it will try to calculate how much ink it has been using), simply remove and reinsert the cartridge and the chip will reset. When the chip resets it will inform the computer that you have inserted a "brand new cartridge".

NOTE: Be careful handling the cartridges by their sides. There is a section of the cartridge that is only covered by a thin plastic film. Puncturing this would cause ink to possible spill out of the side.

Before using the ink, make sure the cap is securely tightened and give the bottle a good shake. Remove the rubber plugs and then fill each cartridge with about 8 - 10 ml of ink. It is recommended to dispense the ink through the provided filter to prevent debris from entering (this project was performed in a clean lab setting so the ink was filtered into a beaker before adding it to the cartridges). Reinsert the plugs and you are ready for printing.

NOTE: The ink filter is NOT the same as the air filter. The filter for the ink is provided with the ink and is much larger.

The first test print is to make sure the printer is not giving you any errors when using 3rd party ink cartridges. After that you need to keep draining the ink until there is no regular ink left in the printer. This can be done by printing full pages of black/color or by selecting the cleaning function (this uses up ink to clean the print head). Keep printing/cleaning until you cannot see any color left. You should only see the dark/metallic looking ink. Once you feel that you have successfully drained the old ink, you can move on to printing circuits.

As previously mentioned, to better your odds of printing a perfect trace you want to get as much ink onto the page as possible. The following settings are to help you do just that:

Media: Transparency

Print Quality: Best

Color Mode: Vivid

Color Enhancement: Enable

Color Density: +2

Improve Pattern Printing: Enable

If possible it is also recommended to use "Photo Mode" and design your circuits with black ink. Photo mode uses Cyan, Magenta, and Yellow to make black instead of just Black by itself. This helps saturate the page with more ink and thus leads to better connections.

Transparencies have proven to be one of the best substrates for printing. The fibers in paper tend to absorb the ink. To make a good connection you need the ink to stay on the surface and bond together. Transparencies are made of cellulose acetate and have no fibers. This makes them the preferred substrate.

The images above show a comparison between the different substrates. The first image is the graphic that is printed, a series of alternating colored lines. The second image is what the print looks like on paper. The third is how the print looks like on the transparency (the side without the quick drying). The fourth picture shows the best printing option with the ink appearing on the quick drying side of the transparency.

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A circuit was designed that utilizes an ATtiny85 to blink a LED on and off. This circuit can be powered from either a 5 V source or a 9 V source with a 5 V regulator. This circuit was drawn up in Fritzing in both breadboard and PCB view. The PCB view was then exported to a PDF file to be printed.

This printer also has the feature of allowing you to insert the pages from the back. This prevents the need for the pages to be flipped when drawing from the conventional paper tray. This can help with a more accurate placement of your circuits. For this method you will want to make sure the "quick drying" side of the transparency is facing upwards as this is the side that will be printed on.

NOTE: The circuit will turn gold in color if it properly forms a conductive trace. If it remains silver then it will not be conductive. If it dries silver then it could mean that the environment is too dry. If a humid environment is not available, the circuits can still be printed using a simple "Fingerprint Method". Repeatedly smudge your fingers on the transparency in the location that the circuit will be printed. The oil from your skin will be enough to make the circuit conductive when it is printed on top of.

TIP: If using the "Fingerprint Method", print out one test of the circuit and put it underneath your transparency. This will help you figure out where you should smudge your print.

A prototype of the desired circuit was first made using a breadboard and an Arduino. The code is just a modified version of the "Blink" example. The code was uploaded to the ATtiny85 that will later be installed in the printed circuit. To learn how to upload code to an ATtiny with an Arduino, check out my in depth tutorial here.

There are a few way to connect components to your printed circuit. The best option that was found in this project was the use of copper tape. Copper tape is both electrically conductive and able to act as an adhesive. This tape is great for making simple connections. Solder was experimented with but it ended up melting both the ink and the substrate.

We also found that some of the parts needed to be bent to make it easier to place with out special tools. Once everything was taped down (not the most precise taping) a voltage was applied and the circuit began to blink the LED on and off as expected.

NOTE: If you used the "Fingerprint Method" you may want to use a Q-Tip to clean off some of the residue around your circuit. This will help the tape stick better.

[1] “Screen printing,” Wikipedia, the free encyclopedia. 27-May-2015.
[2] “Rotogravure,” Wikipedia, the free encyclopedia. 23-May-2015.

[3] “How to Use a Breadboard - learn.sparkfun.com.” [Online]. Available: https://learn.sparkfun.com/tutorials/how-to-use-a... [Accessed: 28-May-2015].

[4] “How-To: Etch a single sided PCB,” Hackaday. .

[5] “imaging.org - Online.” [Online]. Available: https://learn.sparkfun.com/tutorials/how-to-use-a... [Accessed: 28-May-2015].

[6] “The Piezoelectric Effect - Piezoelectric Motors & Motion Systems.” [Online]. Available: https://learn.sparkfun.com/tutorials/how-to-use-a... [Accessed: 28-May-2015].

[7] M. M. Tentzeris, “Inkjet-Printed Nanotechnology-Enabled Zero-Power Wireless Sensor Nodes for Internet-of-Things (IoT) and M2M Applications,” ATHENA Research Group, School of ECE , Georgia Institute of Technology, Atlanta, GA, 30332-250, USA.
[8] Y. Kawahara, S. Hodges, B. S. Cook, C. Zhang, and G. D. Abowd, “Instant inkjet circuits: lab-based inkjet printing to support rapid prototyping of UbiComp devices,” 2013, p. 363.

[9] P. H. King, J. Scanlan, and A. Sobester, “From Radiosonde To Papersonde: The Use of Conductive Inkjet Printing in the Massive Atmospheric Volume Instrumentation System (MAVIS) Project,” 2015.

[10] “NBSIJ - Silver Nanoparticle Ink - 100ml-1,” Mitsubishi Imaging (MPM), Inc. [Online]. Available: http://diamond-jet.com/silvernanoparticleink-2.as... [Accessed: 28-May-2015].

[11] T. Falat, B. Platek, and J. Felba, “Sintering process of silver nanoparticles in ink-jet printed conductive microstructures - Molecular dynamics approach,” 2012, pp. 1/5–5/5.