Flexible, stretchable and wearable electronics have many applications which require them to maintain electromechanical integrity while being repeatedly stretched, bent, and twisted. To study the reliability of these devices, some traditional mechanical test methods have been adapted to include in-situ electrical measurement, including uniaxial tension, twist, and bend, along with several others. One test method which has yet to be fully adapted for flexible and stretchable electronic materials is biaxial tension. A biaxial stress-state can be achieved by directly inflating the substrate. The research presented here focuses on the development of a biaxial inflation test for stretchable substrates and printed conductors under monotonic and cyclic loading conditions. During inflation, electrical performance is monitored via in-situ four-wire resistance measurement. Inflation pressure and resultant surface strain are monitored concurrently using a pressure transducer and three-dimensional digital image correlation, respectively. Two highly stretchable substrate and screen-printed conductor material combinations are examined using the proposed inflation test: silver-flake polymer ink on thermoplastic polyurethane and polymer carbon nanotube composite on platinum-catalyzed silicone. The microstructure of the conductors is examined before, during, and after strain application using a scanning electron microscope. The results of the outer clamp shape on the inflation geometry and resultant strain-state are explored. Experimental results are compared with analytical and finite-element models. Recommendations are then made for material selection, sample design, test procedures, modeling approaches, and analyses of results.


Biaxial Inflation Stretch Test for Printed Flexible Electronics

Division / Sponsors: 
Electronic & Photonic Packaging Division (EPPD)

Paper Proceedings: https://asmedigitalcollection.asme.org/InterPACK/InterPACK2020/volume/84041

InterPACK2020 - Virtual Conference

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.