# Additively Manufactured Polymers for Electronic Components
## 1 Introduction  
There is an increasingly prominent trend of using polymers in the electronics industry, which is currently valued at $5.9 billion. The market is expected to grow to $7.7 billion by 2028, with a projected compound annual growth rate (CAGR) of 3.8%. Polymers are used in the electronics field for various applications, such as flexible electronic circuits, devices, sensors, actuators, light-emitting devices, energy harvesting, and packaging. Conventional processes suited to wafer-scale fabrication of electronics, such as high-temperature doping, vacuum-based deposition, photolithography, and dry or wet etching, are complex and costly, requiring cleanrooms and specialised equipment. By contrast, printing techniques that use liquid inks and simpler, non-vacuum processes offer a promising alternative for scalable and low-cost electronics manufacturing [1]. In the last few years, 3D printing has been utilised to fabricate embedded electronics, 3D structural electronics, conformal electronics, stretchable electronics, and organic light-emitting diodes (OLEDs). Three-dimensional printing applications have significantlyexpanded, and 3D-printed electronics are considered the emerging frontier in additive manufacturing (AM) [2]. New markets and applications have been fostered by the possibility of integrating functional components, such as sensors and circuits, by pausing the printing process at any specific layer [3]. Furthermore, AM technologies can create electronic devices on stretchable, flexible, biocompatible substrates to enhance conformability to irregularly shaped surfaces [4]. Therefore, the application of 3D printing in electronics presents significant potential for the fabrication of complex objects with multifunctional properties. In the context of AM for electronics, polymers are emerging as the material of choice to fabricate flexible electronic devices [3; 5], and they can be either intrinsically or extrinsically conductive [6]. Intrinsically conductive polymers (ICPs), also known as conjugated polymers, have a conjugated \(\pi\)-electron, enabling electron transfer and conductivity. Extrinsically conductive polymers (ECPs) are insulating polymers made electrically conductive by adding fillers, such as metal particles, carbon nanotubes (CNTs), and graphene, which allow electronic transfer [7; 8]. In addition to this, special effort has been channelled into developing thermally conductive polymer nanocomposites that can be additively manufactured [9; 10]. More importantly, insulating polymers are also employed in electronics to avoid short circuits, as well as to protect and isolate devices. These three categories of polymers will be considered in the following section. Moreover, an additional challenge for the electronics industry is how polymeric materials are deposited on the substrate or patterned surfaces. Nowadays, the electronics industry relies on the planar fabrication method mainly through lithographic techniques. Therefore, the fabrication of a third dimension is unexploited, limiting design choices. AM technologies are being studied as alternative fabrication methods. Furthermore, most of the studies in the literature present the use of metallic materials [11; 12], such as silver nanoparticles (NPs) [13], copper [14], CNTs [15; 16; 17], and graphene-based [18; 19] and graphite-based materials [20; 21], for AM owing to their exceptional electrical properties. Of all the materials manufactured via AM for electronics, polymers are the least explored because most electronic components require conductive materials to operate. Therefore, the majority of research and development efforts have been directed toward this specific need. AM has several advantages, such as: (i) the ability to process a large variety of materials, i.e., metals, polymers, and ceramics; (ii) the reduction of waste; (iii) design flexibility; and (iv) the possibility of manufacturing structures and morphologies with peaks, valleys, pillars, or cavities characterised by a considerable height difference.