ADHESION EVALUATION AND ASSEMBLY PROCESS DEVELOPMENT FOR PRINTED SILVER INK ON FLEXIBLE SUBSTRATES

Abstract

Flexible substrates with printed electronics are being increasingly sought for the widespread and cost-effective use of flexible electronics. With printed ink on flexible substrates, several items need to be examined: synthesis of ink, deposition of ink, curing of ink, line and spacing of ink, adhesion of ink, fracture strength of ink, electrical characteristics of ink, etc. Among these items, adhesion of ink to the substrate plays an important role in the overall reliability of printed ink on flexible substrate. In this work, the adhesion and interfacial characteristics of printed conductors were determined though modified shear and peel experimental techniques. Modification to the tests were needed for handling the ink-jet printed films due to manufacturing considerations. (1) These films often are designed to be porous so that the films are more flexible by lower the stiffness. (2) Ink-jetting films often are composed of thin layers that are stacked-up to reach the desired thickness. (3) Depending on the tool and the file conversion to bitmap (or designated file extension) for the printer, the film may show indication of the path taken by the tool head with slight spaces between passes. A numerical model based on sequential crack growth was developed to examine how much the plastic deformation accounts for the experimentally measured peel energy. Lastly, a fully-additive printing process was demonstrated with resistors which resulted in around 6.5 MPa shear strength. For the assemblies, the joint strength of the ink for the joint to traces was stronger than the adhesion strength of the ink to flexible substrate.