Toni Liimatta Inkjet Printing in Manufacturing of Stretchable Interconnects

Smaller form factors and dynamic applications have made flexible circuits an essential part of today’s electronic devices. Although flexible electronics is well established and constantly growing industry, this technology has its limitations. Flexible circuits can typically bend along one axis and cannot therefore conform to arbitrary shapes like for example human skin. The transition to stretchable electronics is an alternative, which can enable bending in any direction simultaneously and in addition dynamically changing the surface area of device. However, manufacturing of stretchable electronics sets new challenges for manufacturing technology due to significantly different material properties of stretchable substrates and therefore new manufacturing methods must be introduced. Inkjet printing is an emerging technology for printed electronics and due to the digital control of the printing process the adaptation to different circuit board layouts is easy and fast. Therefore inkjet printing is especially suitable for small volume manufacturing, prototyping and research purposes of transferring conventional flexible circuits to printing technology. Since inkjet technology has already been proven feasible with flexible circuits, this thesis focuses on evaluating feasibility of inkjet printing in manufacturing of stretchable electronics. Advantages of inkjet technology like contactless deposition, low process temperatures and low use of chemicals are very beneficial when stretchable substrate materials are considered. The feasibility of inkjet printing in manufacturing of stretchable circuits is studied in this thesis through literature review and experimental analysis. Different manufacturing methods for stretchable electronics are reviewed and based on this; a method for manufacturing stretchable devices utilizing inkjet printing and stretchable interconnects is presented. This thesis describes optimizing process of manufacturing process parameters and development of strain testing system to analyze manufactured structures. Peak strain of inkjet-printed conductors on stretchable substrate is found to be modest, but conductivity is observed to be almost fully reversible when strain is released. Based on the knowledge accumulated during this work, suggestions for improving performance of inkjet-printed interconnects on stretchable substrate are given. TAMPERE UNIVERSITY OF TECHNOLOGY Master’s Degree Programme in Electrical Engineering LIIMATTA, TONI: Inkjet printing in Manufacturing of Stretchable Interconnects Master of Science Thesis, 77 pages, 1 Appendix page March 2014 Major: Electronics Product Design Examiner: Assist. Prof. Matti Mäntysalo