Hybridizing additive manufacturing (AM) structures and direct write (DW) deposition of conductive traces enables the design and physical creation of integrated, complex, and conformal electronics such as embedded electronics and complex routing on a fully AM structure. Although this hybridization has a promising outlook, there are several key AM substrate-related limitations that limit the final performance of these hybridized AM-DW electronic parts. These limitations include low-temperature processability (leading to high trace resistivity) and poor surface finish (leading to electronic shorts and disconnections). Recently discovered ultraviolet-assisted direct ink write (UV-DIW) all-aromatic polyimide (PI) provides an opportunity to address these previous shortcomings previously due to its high-temperature stability (450C) and superior surface finish (relative to other AM processes).
The primary goal of this thesis is to characterize the integration of this UV-DIW PI with DW-printed conductive inks as a means for obtaining high-performance hybrid AM-DW electronics. This goal has been achieved through an investigation into the increased temperature stability of AM PI on the conductivity and adhesion of DW extrusion and aerosol jet (AJ) silver inks, determining the dielectric constant and dissipation factor of processed UV-DIW PI, and determining the achievable microwave application performance of UV-DIW PI. These performance measurements are compared to commercially-available PI film and relative to existing AM substrates, such as ULTEM 1010.
The temperature stability of UV-DIW PI enabled higher-temperature post-processing for the printed silver traces, which decreased DIW trace resistivity from 14.94±0.55 times the value of bulk silver at 160 °C to 2.16±0.028 times the resistivity of bulk silver at 375 °C, and AJ silver trace resistivity from 5.27±0.013 times the resistivity of bulk silver at 200 °C to 1.95±0.15 times the resistivity of bulk silver at 350 °C. The adhesion of these traces was not negatively affected by higher processing temperatures, and the traces performed similarly on UV-DIW PI and commercial PI. Furthermore, at similar thicknesses, UV-DIW PI was found to have a similar dielectric constant and dissipation factor to commercial Dupont Kapton PI film from 1 kHz to 1 MHz, indicating its ability to perform highly as a dielectric electronics substrate. Finally, the decrease in resistivity was able to decrease the gap in microwave stripline transmission line performance when compared with ULTEM 1010 processed at 200°C, with peak 10 GHz S21 loss differences decreasing from 2.46 dB to 1.32 dB after increasing the UV-DIW processing temperature from 200 °C to 400°C. / Master of Science / Due to the extensive potential benefits and applications, researchers are looking to hybridize additive manufacturing (AM) processes with direct write (DW) techniques to directly print a 3D part with integrated electronics. Unfortunately, there are several key substrate-related limitations that hinder the overall performance of a part fabricated by hybrid AM-DW processes. Specifically, typical AM materials are not capable of providing an electronics substrate with combined sufficient surface resolution, surface finish, and high-temperature processing stability. However, the recent discovery of a novel AM-processable all-aromatic polyimide (PI) presents an opportunity for addressing these limitations as its printed form offers a high surface resolution, superior surface finish, and mechanical stability up to 400 °C.
The primary goal of this thesis is to evaluate the benefits and drawbacks of this PI, processed via ultraviolet-assisted direct ink write (UV-DIW) AM, as an AM-DW electronics substrate. Specifically, the author characterized the effect of the increased temperature stability of the printed PI on the resultant conductivity and adhesion of silver inks printed via direct ink write (DIW) and aerosol jetting (AJ) DW processes. These results were also compared to the performance of the inks on commercial PI. Furthermore, the dielectric performance of printed PI was evaluated and compared to commercial PI. To demonstrate and evaluate the hybridized approach in a potential end-use application, the author also characterized the achievable microwave application performance of UV-DIW polyimide relative to the existing highest performance commercially available printed substrate material.
The experiments in this thesis found an 83% and 66% decrease in resistivity from extrusion and AJ printed inks due to the ability of the printed PI to be processed at higher temperatures. Furthermore, UV-DIW PI was found to have similar dielectric properties to commercial PI film, which indicates that it can serve as a high-performance dielectric substrate. Finally, the high-temperature processing stability was able to decrease the performance gap in microwave application performance between the higher performing dielectric substrate, ULTEM 1010. These results show that UV-DIW could serve as a dielectric substrate for hybridized AM-DW electronic parts with higher performance and the ability to be deployed in harsher environments than previous AM-DW electronic parts explored in literature.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/101036 |
| Date | 07 December 2020 |
| Creators | Oja, Thomas Edward |
| Contributors | Mechanical Engineering, Williams, Christopher B., Davis, Bradley A., Bartlett, Michael D. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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