Inkjet printing has recently caught the attention of many researchers because of its adaptability to a variety of substrates. Inkjet printing is a non-contact type of printing technology that makes the process of fabrication faster, cheaper, creating less wastage, provide high accuracy and repeatability, do not require high temperatures for fabrication, and facilitate mask free printing, which makes its better-fabricating tool as compared to the traditional printing method of Lithography.Flexible &amp; wearable devices are lately becoming popular among the masses especially in the healthcare domain. Inkjet Printing technology plays a pivotal role in fabricating such devices on flexible substrates because of its adaptability and ability to print on an unconventional flexible substrate like PDMS (Polydimethylsiloxane), PET (Polyethylene terephthalate), Rubbers &amp; other flexible surfaces. Printing on flexible substrates is challenging because of their varying physical and chemical properties. Important substrate properties like surface tension, surface energy, roughness, contamination on the surface, surface topology, environmental factors like temperature and humidity govern the printability on such an unconventional substrate. To print devices on such surfaces, there is a need to modify the surface properties so that desired print can be achieved by plasma treatment with Oxygen, Nitrogen gas, Air, or Chemical reaction methods.&nbsp;Further, Ink used in the Inkjet printer has an important contribution in printing. The inks used for printing electronic circuits should be conductive. Silver and Gold inks are extensively used considering their high chemical stability, good conductivity, and good chemical inertness. Such inks can either be purchased directly from the supplier or can be formulated in the lab with desired properties. These conductive printable inks mainly contain solvents, active materials, and additives. These three components of the ink need to be maintained in the right composition to get printable ink for an inkjet printer. Any changes in the composition of the ink also affect the sintering, curing temperature, and duration of the ink after it's printed on the substrate.Apart from the substrate and ink properties, Inkjet printing parameters also play a crucial role in deciding the quality of the print. Inkjet printing parameters like drop spacing, the temperature of the substrate, nozzle temperature, jetting voltage, velocity, and frequency need to be predetermined and further need to be optimized to get the print of the desired quality.In this article, we investigated the adaptation of multiple commercially available inks and substrates to inkjet printing. &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;We use commercially available silver nanoparticle inks to print electrodes on unconventional substrates through a Fujifilm Inkjet printer&nbsp;DMP-2831. To print, we should match the surface energy of the ink and the substrate. We will first measure the contact angle of this substrate by using a goniometer. In order for the substrate to have good wetting behavior of the substrate, a contact angle, &lt;900&nbsp; is required. Since we are using unconventional substrates to print like PDMS, PET, and Rubbers, which shows poor wettability and high contact angle, it is essential to modify the surface before printing. For surface modification, we perform air plasma treatment on the substrate and recheck the contact angle after treatment. After treating the surface, we printed and cured the silver ink. We measured the conductivity of the printed layer. We designed and tested multilayer printing. After printing and curing the ink, we used the Zygo 3D optical surface profiler to measure the thickness of the layer. Further, we measured the resistance values based upon the geometry i.e., the width, length, thickness of the electrode. Our research helps us understand the variation between the values of resistance of a conductive electrode printed on various unconventional substrates, which can aid us to design the intricate circuits required for flexible and wearable devices.&nbsp;

Inkjet Printing & Conductivity Measurement of Silver Patterns on Flexible Substrates

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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