Extended-Time Process Consistency and Process-Property Relationships for Flexible Additive-Printed Electronics

Abstract

Traditionally, a combination of imaging and plating based subtractive processes have been used for fabrication of printed circuit assemblies to form the needed circuitry on rigid and flexible laminates. In addition to circuits, additive electronics is finding applications for fabrication of sensors for wearable applications and asset situational awareness. Aerosol-Jet printing has shown the capability for printing lines and spaces below $10\ \mu \mathrm{m}$ in width with a wide variety of materials, including nanoparticle inks, conductive polymers, insulators, adhesives, and even biological matter. The adoption of additive manufacturing for high-volume commercial fabrication requires an understanding of the print consistency, electrical and mechanical properties. In this study, the effect of process parameters on the resultant line-consistency, mechanical and electrical properties has been studied for single-layer and multi-layer substrates. Print process parameters studied include the sheath rate, mass flow rate, nozzle size, substrate temperature and chiller temperature. Properties include resistance and shear load to failure of the printed electrical line as a function of varying sintering time and varying sintering temperature. Printed samples have been exposed to different sintering times and temperatures. The resistance and shear load to failure of the printed lines has been measured. The underlying physics of the resultant trend was then investigated using elemental analysis and SEM. The effect of line-consistency drift over prolonged runtimes has been measured for up to 10-hours of runtime. Printing process efficiency has been gauged a function of process capability index (Cpk) and process capability ratio (Cp). Printed samples were studied offline using optical Profilometry to analyze the consistency within the line width, line height, line resistance and shear load to study the variance in the electrical and mechanical properties over time.