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Direct write printing is restricted by the lack of dielectric materials that can be printed with high resolution and offer dissipation factors at radio frequency (RF) within the range of commercial RF laminates. Herein, we outline the development of dielectric materials with dielectric loss below 0.006 in X and Ku frequency bands (8.2−18 GHz), the range required for radio frequency and microwave applications. The described materials were designed for printability and processability, specifically a prolonged viscosity below 1000 cps and a robust cure procedure, which requires minimal heat treatment. In the first stage of this work, nonpolar ring-opening metathesis polymerization (ROMP) is demonstrated at room temperature in an open-air environment with a low-viscosity monomer, 5-vinyl-2-norbornene, using the second-generation Grubbs catalyst (G-II). Differential scanning calorimetry (DSC) was used to study how the catalyst activity is increased with heating at various stages in the reaction, which is then used as a strategy to cure the material after printing. The resulting cured poly(5-vinyl-2-norbornene) material is then characterized for dielectric and mechanical performance before and after a secondary heat treatment, which mimics processing procedures to incorporate subsequent printed conductor layers for multilayer applications. After the secondary heat treatment, the material exhibits a 55.0% reduction in the coefficient of thermal expansion (CTE), an increase in glass-transition temperature (T g ) from 32.4 to 46.1 °C, and an increased 25 °C storage modulus from 428 to 1031 MPa while demonstrating a minimal change in dielectric loss. Lastly, samples of the developed dielectric material are printed with silver overtop to demonstrate how the material can be effectively incorporated into fully printed, multilayer RF applications.

The application of intense pulsed light (IPL) to printed copper nanoparticle (CuNP) films enables rapid curing on low temperature substrates in ambient conditions. In this work, we printed CuNP ink on liquid crystal polymer (LCP; Vectra A resin) and then cured the films using a high energy density light pulse. High-resolution SEM images of the cured films revealed that the CuNPs on LCP were fused together. Optimal curing parameters were a 5 ms pulse, 75% duty cycle, and an energy density range of 4.2–5.2 J⋅cm-2. Sheet resistance, Rs, values as low as ~0.1 Ω⋅sq-1were obtained. The LCP substrate took on a yellowed appearance after the application of five pulses and exhibited a surface free energy increase. A filter that blocked wavelengths <450 nm was placed over the printed copper film on LCP. As expected, the presence of the filter decreased the total energy density and produced a cured film with high Rs; however, when the energy density was increased in the presence of the filter, the Rs remained high (0.95 Ω⋅sq-1). This preliminary work indicates that additional studies are required not only to understand low thermal budget curing on LCP, but also to elucidate the properties of substrates that enable low Rs.

No abstract

Here, we report a previously un-reported printed electronics/additive manufacturing (AM) approach to fabricate conductive/resistive features on novel insulating silver–barium strontium titanate (Ag–BST) printed composite films. Ag–BST composite functional ink was formulated by blending a conductive Ag nanoparticle ink and an insulating BST nanoparticle ink. The blending ratio of Ag and BST inks was optimized to obtain the insulating phase after the initial curing and the conductive/resistive phase following selective laser sintering under ambient conditions. Selective laser sintered Ag–BST resistors showed an ohmic behavior and the resistivity could be adjusted by varying the laser sintering parameters, such as the wavelength, power and the rastering speed/pitch of the laser. This insulator to conductor/resistor transitioning Ag–BST ink paves a new path for direct write printed electronics/AM applications. Proofs of concept for potential applications utilizing this functional ink are demonstrated. Also, this Ag–BST ink can be used as a conventional resistive ink for dispensing printers. Thermally sintered Ag–BST resistors showed less than 8% variation in resistance between −50 °C and 150 °C.