# Additively Manufactured Polymers for Electronic Components
## 3 Polymers Used for AM in Electronic Applications
### Insulating Polymers  
Insulator materials with high thermal conductivity are becoming promising for electronic applications because standard metallic materials have limitations such as high cost, weight, and electrical conductivity. This has led to the additive manufacturing of different polymer-based nanocomposites containing boron nitride particles for effective thermal management in electronic devices [9; 10; 65; 67; 123; 124]. Moreover, the dielectric properties of insulating layers in high-density interconnects can significantly influence the performance of electronic circuits and signal propagation speed. Indeed, the polarity of dielectric materials can limit signal propagation speed and the maximum interconnect density on a chip. Furthermore, lower dielectric permittivity enables closer spacing of interconnect lines, reducing crosstalk and increasing device layout density. Therefore, the use of insulating layers with lower dielectric constants (low-k), such as low-k polymer materials, can boost circuit density and speed, making them suitable for cost-effective, high-performance circuits [125]. Benzocyclobutene (BCB)-based materials have gained significant commercial interest due to their low dielectric constants, making them suitable as dielectrics in on-chip connections, such as resin-coated copper foil. Moreover, BCB-based polymers are thermally activated and are obtained as clean reaction products of highly reactive units in precisely controlled curing processes. This is particularly notable in lithography materials, where the control over linear polymers as precursors and the accuracy and reactivity of benzocyclobutene units have resulted in low-error materials [126]. Dow Chemical Co. has developed a range of low-k polymers that are based on various benzocyclobutene monomers, also known as BCB (biscyclo[4.2.0]octa-1,3,5-triene or 1,2-dihydropyobenzocyclobutene). One of their commercial products is CYCLOTENE, which is a family of thermsetting polymers derived from the monomer 1,3-divinyl-1,1,3,3-tetramethyldisiloxane-bis-benzocyclobutene (DVS-bis-BCB), as depicted in Figure 9. In many instances, CYCLOTENE is simply referred to as BCB in the literature. BCB has been specifically designed for electronic coating applications due to its low-k characteristics, making it ideal as an interlayer dielectric in radio frequency components. Since the early 1990s, it has been widely used in applications such as bumping and redistributing chips, planarisation in flat panel displays, MEMS hermitisation, wafer bonding, passivation, and gap filling. Its versatility comes from its properties, including effective planarisation, minimal outgassing, and low copper migration [127]. Regarding BCB's fundamental electrical parameters, such as dielectric constant (k), loss tangent (tan \(\delta\)), and breakdown strength, which are critical for the performance of advanced electronic devices, BCB-based materials exhibit an ultra-low k that is between 2.65 and 2.43 in the range of 1 MHz and 1 THz, combined with a very low loss tangent in the range of 0.0008-0.002 [128], which minimises electrical energy losses due to parasitic capacitive effects [129]. The moisture-induced dielectric constant increases by just \(\sim\)1.2% in 85 \({}^{\circ}\)C/85% RH, and the breakdown strength ranges from \(\sim\)2.25 MV/cm to 3.2 MV/cm, with varying electrode spacing. Compared to other dielectric materials, BCB's properties enable increased signal propagation velocity with lower crosstalk, closer interconnection spacing, and negligible dependency on moisture absorption, which are essential in electronic circuits and high-density on-chip interconnects [125]. AM of BCB-based material with IJP and AJP was recently presented. BCB was used with AM technologies for the first time in two studies by our research group, which investigated the processing of this polymer using IJP and AJP. Regarding IJP, an in-depth study was conducted on the ink properties and processing parameters [130].