# Additively Manufactured Polymers for Electronic Components
## 1 Introduction
Once on the surface, the droplets solidify either by evaporation, cooling, or chemical curing, depending on the ink's composition. Aerosol jet printing (AJP) is a novel fabrication technology that belongs to this group. It relies on focusing an aerosol stream of the material under consideration on a substrate [25,30,31]. AJP uses a directed aerosol stream to ensure consistent deposition (Figure 1e) [32]. It is a non-contact technique, and the nozzle is placed from 1 mm to 5 mm away from the substrate [33]. This approach enables precise patterning of more intricate surfaces [34]. AJP is a technique for the exact digital placement of droplets in precisely defined positions. There are two main types of AJP systems based on the atomisation method, namely, the ultrasonic and the pneumatic AJP [35]. In principle, the AJP technique is compatible with any material that can be suspended within an aerosol. Commercial systems employ ultrasonic or pneumatic atomisation to create aerosols from inks with viscosities spanning from 1 mPas to 1000 mPas. The working principle involves generating a fine mist of droplets, and then focusing this mist into a narrow stream by using a surrounding sheath gas. This focused aerosol jet can be precisely guided onto the substrate, making it ideal for printing fine features, even on irregular surfaces, with minimal overspray. Material extrusion processes encompass AM technologies based on the continuous flow of inks or melted polymeric filaments through a nozzle (Figure 1d) [23]. The deposition of inks is also referred to as direct ink writing (DIW) [36, 37, 38]. Ink filaments are deposited layer by layer until the entire structure is created. This technology offers several advantages, including flexibility and low processing costs. It operates at room temperature. However, the materials used in this process typically have poor mechanical properties, with the subsequent need for the addition of reinforcement fillers [23; 24]. Specific rheological properties are required to print polymeric inks using DIW [39; 40]. The ink should be shear-thinning, i.e., the viscosity decreases with increasing applied shear rate or deformation, thus allowing proper extrusion of the material. Furthermore, the ink should also have a sufficiently high zero-shear rate viscosity, i.e., the viscosity of the material when no deformation is applied, to keep its shape after the extrusion process. The ink is pushed through a nozzle using air pressure or a mechanical plunger and, once extruded, its rheological behaviour ensures it retains its shape. Depending on the formulation, the material solidifies by light-induced curing, solvent evaporation, or heat, allowing the printed shape to set as it builds up layer by layer. After the deposition of the material on the substrate, the ink needs to solidify. Solidification can happen upon UV irradiation to cross-link a photopolymer by solvent evaporation or by thermal curing. The process of material extrusion for melted polymers is known as fused deposition modelling (FDM), also referred to as fused filament fabrication (FFF). This method involves melting and extruding a thermoplastic polymer. A solid filament is fed into a heated nozzle where it melts. The molten polymer is then deposited in thin strands that cool and solidify upon contact with the built surface. As each new layer is laid down, thermal bonding occurs between layers, helping to form a cohesive, three-dimensional object. Other AM technologies have recently begun using polymeric materials, such as laser-induced forward transfer (LIFT) technology. LIFT is a printing process that allows the deposition of solid and liquid materials with high resolution. [PERSON] et al. presented it for the first time almost 30 years ago (Figure 1f) [41]. Since then, various LIFT-based methods have emerged to customise the process according to the printing material properties and application requirements.