De fundamenten en technologische inzichten van Aerosol Jet® Printing

Printed Electronics (PE) has emerged as a transformative manufacturing technique, offering a alternative methods to fabricate flexible, low-cost, and conformable electronic devices that are not achievable with conventional silicon-based, subtractive methods. PE in a nutshell refers to deposition of functional materials, onto a substrate via different printing methods, in order to fabricate an electronic circuit. Among the diverse portfolio of PE printing techniques, Aerosol Jet® Printing (AJ®P or AJP) has distinguished itself as a uniquely versatile direct-writing technology. It is capable of depositing a wide range of functional inks with high resolution on both flat and non-planar substrates. It is a key enabler for applications in smart packaging, biomedical sensors, and next-generation communication systems. However, despite its significant potential, the widespread industrial adoption of AJP is hindered. The main challenges lies in process reliability, robustness, and predictability. The AJP process is broadly categorized into four major sub-processes: (i) atomization, (ii) transportation, (iii) collimation and in-flight jet, and (iv) impaction and impingement. The complex interplay of aerosol generation, in-flight jet dynamics, and on-substrate impingement is governed by various interdependent parameters. Until now, process optimization has mostly relied on empirical, trial-and-error methodologies or on computational models built upon theoretical assumptions for critical physical parameters, such as in-flight droplet size and velocity. This fundamental gap in experimental validation has meant the AJP process is often treated as a 'black box,' preventing the establishment of a predictive, physics-based understanding required for reliable and optimized manufacturing. A part of this doctoral thesis addresses this knowledge gap by conducting an experimentally-driven investigation into the fundamental physics of the AJP process. The research aims to decode the process chain by providing the first direct, in-situ measurements of key aerosol jet properties. Then, by using this foundational data to establish a predictive framework for process control. This framework is then applied to the fabrication and validation of industry-relevant functional devices, thereby bridging the gap between fundamentals and practical application. The core of this fundamental research involves the novel integration of measurement tools with a commercial AJP system. Phase Doppler Anemometry (PDA) was employed to perform the first-ever experimental characterization of in-flight aerosol droplet size and velocity for metallic silver nanoparticle (AgNP) ink and a conductive polymer (PEDOT:PSS) ink. For the AgNP ink, the mean droplet diameter (d₅₀) was measured to be in the range of 1.87 µm to 6.60 µm, while droplet velocities ranged from 11.85 m/s to 54.97 m/s. For PEDOT:PSS ink, mean droplet diameter (d₅₀) was measured to be in the range of 3.12 µm to 4.54 µm, while droplet velocities ranged from 14.22 m/s to 46.01 m/s. These basic measurements allows the calculation of key dimensionless numbers (Reynolds, Weber, Stokes), providing a quantitative basis for understanding the jet's hydrodynamic regime or jet behaviour. Furthermore, optical imaging was used to measure the in-flight jet width, which was then correlated with the final on-substrate printed linewidth. This is the first attempt to create a correlation between the machine parameters such as gas flow, the jet characteristics such as droplet size present in it, jet velocity, jet width, and the linewidth of the printed tracks from the same jet. It was confirmed that the gas flows ratio (also known as Focusing Ratio -FR) critically plays the role in the jetwidth (JW) and the printed linewidth (LW). But, this study also reveals that the role of AGF is also present in the LW apart from FR. The correction model is formulated to validate the experimental findings in alignment with the relevant literature. These fundamental insights were subsequently applied to develop and validate three distinct proof-of-concept demonstrators. First, a printed RFID antenna (13.56 MHz) using a silver ink was fabricated and tested on a fibre-based paper substrates. A systematic methodology for was established for successful fabrication of a RFID antenna. The methodology consists of substrate selection out of 16 acquired substrates, the electrical performance of the silver ink on 16 different papers, the challenges of the paper substrate on thermal sintering, and the several testing for the reliability of the printed tracks. The final printed antenna achieved the prerequisite for a fully functional antenna with a low resistance of 27 &Omega; and an inductance of 2.57 µH. Second, the technological complexity was elevated by demonstrating multi-material printing to create an RFID-assisted Critical Temperature Indicator (CTI) showing AJP versatility. This intelligent label integrated the printed antenna with an irreversible CTI using a custom-formulated, AJP-compatible polyaniline (PANI) ink. After the formulation of the ink, it was characterized using UV-vis to investigate its oxidation states. AJP was employed to print silver and customized AJP ink on to the paper substrate. The activation of the PANI using an acid was critical to activate the printed label. After the activation, the indicator provided both a visual (blue-to-green) and electronic (R > 1 M&Omega; to R < 30 k&Omega;) indication. The testing and verification of RFID antenna was also performed successfully. Due to the unavailability of the functional materials (such as piezo-resistive inks), hybrid manufacturing was needed in order to fabricate a pressure sensor. The research validated a hybrid manufacturing workflow using SLS, AJP, and stencil printing to produce a fully printed piezoresistive pressure sensor on a 3D polyamide substrate. It demonstrated a dual-regime sensitivity (106.79 &Omega;/MPa in the high-sensitivity region and 7.65 &Omega;/MPa in the low-sensitivity region). Hysteresis and time-drift tests were successfully conducted to assess the sensor's industrial potential. In summary, this thesis provides a foundational, experimentally-validated understanding of the AJP process, especially sub-process iv, moving it from a 'black box' to a more predictable and controllable prototyping technique. The successful fabrication of functional devices in smart packaging, and biomedical sensing demonstrates the direct applicability of these fundamental insights. This work not only contributes to the scientific literature but also provides a practical implementation of AJP in next-generation electronic applications.