As the need for high-speed electronics continues to rise rapidly, printed wiring board (PWB) requirements become ever-more demanding. A typical PWB is fabricated by bonding dielectric films such as polyimide to electrically conductive copper foil such as rolled annealed (RA) copper and is expected to become thinner, flexible, durable, and compatible with high-frequency 5G performance. Polyimide films inherently feature a higher coefficient of thermal expansion (CTE) than copper foils; this mismatch causes residual thermal stresses. To attenuate the mismatch, silica nanoparticles may be used to reduce the CTE of PI. A nodulated copper surface can be used to enhance the Cu/PI adhesion by additional bonding mechanisms that could include a type of mechanical bonding, which is a focus of this study. In this investigation, a 90° peel test was used to measure the peel strength in copper/polyimide/copper laminates containing nodulated copper and polyimide reinforced with 0, 20, and 40 wt % silica nanoparticles. The influence of silica nanoparticles on the peel strength was quantitatively evaluated. Laminates incorporating polyimide films lacking silica nanoparticles had a â¼3.75× higher peel strength compared with laminates reinforced with 40% silica. Their failure surfaces were analyzed by using scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX), and X-ray photoelectron spectroscopy to identify the mode of failure and to understand bonding mechanisms. The key bonding mechanism, mechanical interlocking, was achieved when the polyimide surrounded or engulfed the copper nodules when the laminate was created. Post-testing failure surface analysis revealed the presence of copper on the polyimide side and polyimide on the copper side, indicating mixed mode failure. An analytical model was developed to determine the impact of applied pressure, temperature, and time on the polyimide penetration and mechanical interlocking around the copper nodules. The model was validated by measuring the peel strength on another set of specimens fabricated using increased temperature and pressure that showed a 3× increase in peel strength compared to lower temperature/pressure processing conditions. This enhanced adhesion resulted from the lower polymer material viscosity at higher temperatures, which fosters deeper and more complete penetration around the copper nodules during processing at higher pressures for longer durations. The methodology of combining peel testing, viscosity and CTE measurement, SEM/EDX, surface chemical analysis, and penetration depth calculation developed herein enables the calculation of the desired processing parameters to enhance functionality and improve adhesion.
2D covalent organic frameworks (2D COFs) are a unique materials platform that combines covalent connectivity, structural regularity, and molecularly precise porosity. However, 2D COFs typically form insoluble aggregates, thus limiting their processing via additive manufacturing techniques. In this work, colloidal suspensions of boronate-ester-linked 2D COFs are used as a spray-coating ink to produce large-area 2D COF thin films. This method is synthetically general, with five different 2D COFs prepared as colloidal inks and subsequently spray-coated onto a diverse range of substrates. Moreover, this approach enables the deposition of multiple 2D COF materials simultaneously, which is not possible by polymerizing COFs on substrates directly. When combined with stencil masks, spray-coated 2D COFs are rapidly deposited as thin films larger than 200 cm2 with line resolutions below 50 µm. To demonstrate that this deposition scheme preserves the desirable attributes of 2D COFs, spray-coated 2D COF thin films are incorporated as the active material in acoustic sensors. These 2D-COF-based sensors have a 10 ppb limit-of-quantification for trimethylamine, which places them among the most sensitive sensors for meat and seafood spoilage. Overall, this work establishes a scalable additive manufacturing technique that enables the integration of 2D COFs into thin-film device architectures.
Functionalized diazatetracenes are prepared using a new two-step sequence. The use of a dichlorobenzaldehyde in a Cu-catalyzed benzannulation of acetylenes provides functionalized dichloronaphthalenes that afford diazatetracenes using Buchwald-Hartwig aminations. This approach provides unique substitution patterns and rapid access to covalently linked dimeric diazatetracenes. Their electronic properties are characterized by UV-vis absorption/emission and cyclic voltammetry, revealing strong effects from both external stimuli by acid and internal substituent effects.
The low conductivity of two-dimensional covalent organic frameworks (2D COFs), and most related coordination polymers, limits their applicability in optoelectronic and electrical energy storage (EES) devices. Although some networks exhibit promising conductivity, these examples generally lack structural versatility, one of the most attractive features of framework materials design. Here we enhance the electrical conductivity of a redox-active 2D COF film by electropolymerizing 3,4-ethylenedioxythiophene (EDOT) within its pores. The resulting poly(3,4-ethylenedioxythiophene) (PEDOT)-infiltrated COF films exhibit dramatically improved electrochemical responses, including quantitative access to their redox-active groups, even for 1 µm-thick COF films that otherwise provide poor electrochemical performance. PEDOT-modified COF films can accommodate high charging rates (10-1600 C) without compromising performance and exhibit both a 10-fold higher current response relative to unmodified films and stable capacitances for at least 10â¯000 cycles. This work represents the first time that electroactive COFs or crystalline framework materials have shown volumetric energy and power densities comparable with other porous carbon-based electrodes, thereby demonstrating the promise of redox-active COFs for EES devices.
