Additive-Manufactured Stochastic Polyimide Foams for Low Relative Permittivity, Lightweight Electronic Architectures

Abstract

Polyimides are widely utilized engineering polymers due to their excellent balance of mechanical, dielectric, and thermal properties. However, the manufacturing of polyimides into complex multifunctional designs can be hindered by dimensional shrinkage of the polymer upon imidization and post processing methods and inability to tailor electronic or mechanical properties. In this work, we developed methods to three-dimensional (3D) direct ink write polyimide closed-cell stochastic foams with tunable densities. These polyimide structures preserve the geometrical fidelity of 3D design with a linear shrinkage value of <10% and displayed microscale porosity ranging from 25 to 35%. This unique balance of morphology and direct-write compatibility was enabled by polymer phase inversion behavior without the need of conventional post-print cross-linking, imidization, or poreinducing freeze processing. The manufacturability, thermal stability, and dielectric properties of the 3D polyimide stochastic foams reported here serve as enablers for the exploration of hierarchical, lightweight, high-temperature, high-power electronics.

Sustainable Dielectric Films with Ultralow Permittivity from Soluble Fluorinated Polyimide

“…The sPI film with a porosity rate of 71%, which was fabricated by using pure DMF as the solvent, displayed the smallest k of 1.51 at 10 5 Hz. We also calculated the permittivity of the porous sPI films using two appropriate rules of mixtures (Maxwell–Garnett (MG) and Looyenga–Landau–Lifshitz (LLL)) [ 38 , 45 ]. These two models are suitable for a mixture that has spherical air inclusions ( k = 1) in the polymer matrix.…”

“…Consequently, the incorporation of air, which has an extremely low dielectric constant of nearly 1.0, can significantly reduce the dielectric constant of resulting porous sPI. However, thus far, relatively few studies have been conducted along this path to develop low- k sPI films [ 36 , 37 , 38 ]. As a comparison, a significant amount of research has focused on the fabrication of conventional thermosetting polyimides with low k by introducing porosity [ 39 , 40 , 41 , 42 ].…”

A promising low‐dielectric‐constant material with good comprehensive performance upon heating

“…As one of the most effective ways to greatly reduce the dielectric constant of materials, the introduction of porous structure is often involved because it can accommodate a large amount of air with the lowest dielectric constant. [19][20][21][22][23] 23 A metal-organic framework of [Cu 3 (BTC) 2 ] n with highly porous structure was incorporated into cellulose nanofibrils through the solution-based strategy to prepare an ultra-low dielectric films. 24 PI aerogels in which dodecyldiamine in place of dimethylbenzidine were also prepared.…”

Porous structure contained polyimide film with enhanced dielectric properties upon high temperature

“…[32][33][34][35] Aerogels and foams with high porosity were the mostly constructed porous structures which help to decrease the dielectric constant of polymer materials. [36][37][38][39] The syndiotactic polystyrene aerogel prepared from a simple freeze casting approach exhibited a very low dielectric constant close to that of air. Polyarylene ether nitrile and polyarylene ether nitrile/SiO 2 foams with bi-modal pore structure were fabricated via delayed phase inversion and supercritical carbon dioxide batch foaming, respectively, to acquire the low-dielectric-constant materials with increased elongation at the break.…”

“…The introduction of porous structure can incorporate large amount of air, which has the lowest dielectric constant of 1, into the polymer material, combined with the scaling down of dipole density, thus greatly reduce the dielectric constant of polymer materials 32–35 . Aerogels and foams with high porosity were the mostly constructed porous structures which help to decrease the dielectric constant of polymer materials 36–39 . The syndiotactic polystyrene aerogel prepared from a simple freeze casting approach exhibited a very low dielectric constant close to that of air.…”