Effect of Gas Flow Rates on Quality of Aerosol Jet Printed Traces With Nanoparticle Conducting Ink

This paper focuses on the influence of carrier gas flow rate (CGFR) and sheath gas flow rate (SGFR) on the quality of conductive traces printed with nanoparticle inks using aerosol jet printing (AJP). This investigation was motivated by previous results of two AJP specimens that were printed at different gas flow rates and yielded significantly different thermal cycling durability lifetimes. A parametric sensitivity study was executed by printing and examining serpentine trace structures at 15 different combinations of CGFRs and SGFRs. The analysis included quantifying the trace's macroscale geometry, electrical properties, and micromorphological features. Interesting macroscale results include an increase in effective conductivity with increasing CGFR. At the microscale, image processing of high magnification scanning electron microscope (SEM) images of the printed traces revealed that agglomerations of silver clusters on the surface of traces became coarser at higher CGFR and also that agglomerates in the bulk were finer than those on the surface. Crystalline silver deposits were observed at all flow rates. In addition, cross sectioning of the printed traces showed higher incidences of buried cohesive cracking at higher gas flow rates. These cohesive cracks reduce the robustness of the traces but may not always be visible from the surface. The degree of cohesive cracking was seen to be broadly correlated with the coarseness of the surface agglomerates, thus suggesting that the coarseness of surface agglomerates may provide a visible surrogate measure of the print quality. The results of this study suggest that print quality may degrade as gas flow rates increase.