Direct writing of silver systems: controlling dimension and delamination for multimaterial printing
Creators: name: Kondapalli, Satya Sweta
Publisher: name: No Publisher Supplied
Year: 2022

description: Multilayer ceramics composites are currently manufactured using a combination of multitude processes ranging from tape casting, screen printing, and mechanical pressing. The process produces material waste while producing the product such as the cavities punched into the green tape, and ink waste in screen printing, and in the processing techniques to customize the product such as the dies and stencils required for each part. Utilizing additive manufacturing to create the multilayer ceramic composites could reduce the material waste by depositing the ink exactly and allowing for easy changes in design. While Stereolithography (SLA) can be utilized to create high resolution multilayer ceramic parts, combining it with a second material introduces challenges of cross contamination between the two materials. Instead, by combining two different types of additive manufacturing, SLA and Direct writing (DW) specifically, this issue can be mitigated. However, multilayer ceramic and metal inks suffer from delamination.The goal of the dissertation is to develop conductive inks for DW with high level of dispersion, dimensional control, to use in multilayer ceramic composites. To achieve this goal, five objectives were designed to achieve the goal: identifying and understanding the parameters that affect direct writing, developing ink with proper rheological properties, studying cure depth to reduce the dependency on rheological properties, and printing single layer and multilayer metal parts. Finally, the knowledge gained from the previous objectives culminate in the objective to print multimaterial multilayer parts.Two different ink types were studied, one based on screen printing vehicles and another based on photocurable vehicles. Important observations in understanding the parameters, led to the realization for the need of constrained rheological properties i.e., the need for high viscosity and time dependent recovery to prevent line relaxation. High rate of relaxation on the substrate due to incompatibilities between the ink vehicle and the substrates’ binder were observed. This could cause the prints to lose feature resolution. To reduce the impact of time based relaxation, a photocurable silver ink system which could solidify the feature before relaxation could begin, was decided as the ideal candidate system. However, when dealing with the photocurable system, cure depth also needs to be taken into consideration.A two pronged approach was used to achieve ideal photocurable silver inks. The first prong dealt with targeting the required rheological properties such as maximizing the viscosity and ensuring shear thinning behavior. This study helped establish the printable viscosity range as 28,480-710,550 cP for the printer system, which meant a solid content range of 25 vol.% to 55 vol.%. The second prong dealt with maximizing cure depth by looking into compositional and processing variables. As cure depth is affected by scattering and absorption, which in turn are dependent on powder particle size, powder solid content, incident energy doses, types of photoinitiators were varied and their effect on cure depth was studied. The findings indicated that a low solid content ink, with larger particles would be ideal for maximizing the cure depth. By increasing the energy dose, a higher depth of cure was achieved in some powders.An intersection ink that satisfied the rheological constraints and the compositional constraints to maximize cure depth was identified from the two prongs. Both single layer and multilayer materials were printed and were fully cured. A proof of concept of a multimaterial print was also conducted by combining SLA and Direct Writing, creating a multilayer ceramic with metal interconnects.