Thermally Stable Siloxane Hybrid Matrix with Low Dielectric Loss for Copper-Clad Laminates for High-Frequency Applications

Flexible Copper Films Modification via Spontaneous Reduction of Aryldiazonium Gold Salts: Unraveling Surface Properties and Energy Profile

In this study, we report the modification of flexible copper films via the spontaneous reduction of aryldiazonium gold salts [X-4-C6H4N≡N]AuCl4 (X═COOH, NO2). The electroless modification involves dipping of flexible copper films in the aryldiazonium gold solutions for a few seconds, under ambient conditions, followed by a washing step with deionized water to obtain a mechanically robust gold-aryl coating. The chemical composition, morphology, electronic structure, and optical properties of the gold-aryl layer and the flexibility of the modified copper films are supported by the results from X-ray photoelectron spectroscopy (XPS), electrochemistry, contact angle, scanning electron microscopy (SEM), and ultraviolet photoelectron spectroscopy (UPS). XPS surface analysis showed metallic gold in addition to C-C, C-O/C-N, and C═O functional groups from the grafted aryls. Cu 2p showed metallic copper as a major component and a small amount of Cu(II) ions. Wettability studies showed that Au-COOH@Cu increased the contact angle of the bare copper films from 68.0 ± 0.7° to 82.0° ± 0.7°, while Au-NO2@Cu increased the contact angle to 134.0° ± 0.3°. UPS energy profile analysis of [HOOC-4-C6H4N≡N]AuCl4 (valence band maximum = 1.91 eV) exhibited greater reducibility than [O2N-4-C6H4N≡N]AuCl4 (valence band maximum = 2.91 eV). The lower ionization potential of [HOOC-4-C6H4N≡N]AuCl4 (IP = 4.33 eV) enhanced the reactivity upon copper film contact, potentially inducing efficient energy level alignment, compared with [O2N-4-C6H4N≡N]AuCl4 (IP = 5.62 eV). UPS results were further supported by electrochemistry investigation which revealed that [HOOC-4-C6H4N≡N]AuCl4 is easily reducible compared with [O2N-4-C6H4N≡N]AuCl4. The findings presented here hold significant implications for developing flexible copper films and pave the way for future advancements in electronic material modification for industrial applications.

Enhancing the dielectric and thermal properties of polytetrafluoroethylene-based composites through designing and constructing a novel interfacial structure

Polytetrafluoroethylene (PTFE) is widely used as a fundamental core material for high-frequency and high-speed signal transmission fields due to its excellent dielectric properties. However, the high coefficient of thermal expansion (CTE) characteristic of PTFE severely limits its practical application. The CTE of PTFE can be reduced by filling with SiO2, which is always accompanied by a rapid deterioration of dielectric properties due to the poor interfacial compatibility between SiO2 and PTFE matrix. In this paper, the challenge of synergistic regulation of dielectric and CTE properties for PTFE-based composites is overcome by constructing an interfacial structure with physical interactions. Micro-mesoporous SiO2 (mSiO2) is prepared and introduced as a filler, compared with smooth surface SiO2 (sSiO2), the presence of micro-mesoporous in mSiO2 allows PTFE molecular chains to be adsorbed on the surface or in the pore channels of mSiO2, which improves the interfacial combination of the mSiO2/PTFE composites through the physical interaction between mSiO2 and PTFE. The results show that mSiO2/PTFE composite exhibits a lower CTE (58 ppm °C-1) while maintaining a lower dielectric constant (εr, 2.29, 30 GHz) with dielectric loss (tan δ, 2.31 × 10-3, 30 GHz) at a filler addition of 30 vol%, as compared with that of the sSiO2/PTFE composites. This work provides a new strategy for fabricating PTFE-based composites with low CTE as well as low εr and tan δ.

Phosphorus-Containing Flame-Retardant Benzocyclobutylene Composites with High Thermal Stability and Low CTE

As a component of printed circuit substrate, copper clad laminate (CCL) needs to meet the performance requirements of heat resistance, flame retardancy, and low coefficient of thermal expansion (CTE), which, respectively, affects the stability, safety, and processability of terminal electronic products. In this paper, benzocyclobutylene (BCB)-functionalized phosphorus-oxygen flame retardant composites were prepared through introducing the BCB groups, and the performance was researched by thermogravimetric analysis, microcombustion calorimetry, and thermomechanical analysis. The research results show that these phosphorus oxide compounds containing BCB groups show good thermal stability and low total heat release (THR) after thermal curing, and the more BCB groups on the phosphorus oxide monomers, the better the thermal stability and flame retardancy of cured resins. The T_d5 and THR of the composite (M3) are as high as 443 °C and 23.1 kJ/g, respectively. In addition, the CTE of M3 is as low as 16.71 ppm/°C. Introduction of BCB groups which can be crosslinked through heat to improve the thermal stability, flame retardancy, and reduced CTE of traditional organophosphorus flame retardant materials. These materials are expected to be good candidates for CCL substrates for electronic circuits.

Progress in Polymer-Ceramic Hybrid Antifouling Coatings

Simultaneous realization of superior mechanical and antifouling properties is critical for a coating. The use of stereoscopic polysiloxanes in place of linear polysiloxanes to fabricate antifouling coatings can combine properties of organic and inorganic materials, i.e., they can exhibit both high hardness and wear resistance from inorganic components as well as the flexibility and tunability from organic components. This strategy is used to prepare hard yet flexible antifouling coatings or polymer-ceramic hybrid antifouling coatings. In this mini-review, we report the recent advances in this field. Particularly, the effects of stereoscopic polysiloxane structures on their mechanical and antifouling properties are discussed in detail.

Siloxane Hybrid Material-Encapsulated Highly Robust Flexible μLEDs for Biocompatible Lighting Applications

Flexible micro-light-emitting diodes (f-μLEDs) have been regarded as an attractive light source for the next-generation human-machine interfaces, thanks to their noticeable optoelectronic performances. However, when it comes to their practical utilizations fulfilling industrial standards, there have been unsolved reliability and durability issues of the f-μLEDs, despite previous developments in the high-performance f-μLEDs for various applications. Herein, highly robust flexible μLEDs (f-HμLEDs) with 20 × 20 arrays, which are realized by a siloxane-based organic-inorganic hybrid material (SHM), are reported. The f-HμLEDs are created by combining the f-μLED fabrication process with SHM synthesis procedures (i.e., sol-gel reaction and successive photocuring). The outstanding mechanical, thermal, and environmental stabilities of our f-HμLEDs are confirmed by a host of experimental and theoretical examinations, including a bending fatigue test (10⁵ bending/unbending cycles), a lifetime accelerated stress test (85 °C and 85% relative humidity), and finite element method simulations. Eventually, to demonstrate the potential of our f-HμLEDs for practical applications of flexible displays and/or biomedical devices, their white light emission due to quantum dot-based color conversion of blue light emitted by GaN-based f-HμLEDs is demonstrated, and the biocompatibility of our f-HμLEDs is confirmed via cytotoxicity and cell proliferation tests with muscle, bone, and neuron cell lines. As far as we can tell, this work is the first demonstration of the flexible μLED encapsulation platform based on the SHM, which proved its mechanical, thermal, and environmental stabilities and biocompatibility, enabling us to envisage biomedical and/or flexible display applications using our f-HμLEDs.

Controlled Vertically Aligned Structures in Polymer Composites: Natural Inspiration, Structural Processing, and Functional Application

Vertically aligned structures, which are a series of characteristic conformations with thickness-direction alignment, interconnection, or assembly of filler in polymeric composite materials that can provide remarkable structural performance and advanced anisotropic functions, have attracted considerable attention in recent years. The past two decades have witnessed extensive development with regard to universal fabrication methods, subtle control of morphological features, improvement of functional properties, and superior applications of vertically aligned structures in various fields. However, a systematic review remains to be attempted. The various configurations of vertical structures inspired from biological samples in nature, such as vertically aligned structures with honeycomb, reed, annual ring, radial, and lamellar configurations are summarized here. Additionally, relevant processing methods, which include the transformation of oriented direction, external-field inducement, template method, and 3D printing method, are discussed in detail. The diverse applications in mechanical, thermal, electric, dielectric, electromagnetic, water treatment, and energy fields are also highlighted by providing representative examples. Finally, future opportunities and prospects are listed to identify current issues and potential research directions. It is expected that perspectives on the vertically aligned structures presented here will contribute to the research on advanced multifunctional composites.

An effective strategy for the preparation of intrinsic low-k and ultralow-loss dielectric polysiloxanes at high frequency by introducing trifluoromethyl groups into the polymers

Two new CF₃-containing polysiloxanes with low dielectric constant (D_k) and dielectric loss (D_f ) at a high frequency of 5 GHz were reported. The sample with two −CF₃ groups exhibits better dielectric properties with D_k of 2.53 and ultralow D_f of 1.66 × 10⁻³.

Efficient and Adhesiveless Metallization of Flexible Polyimide by Functional Grafting of Carboxylic Acid Groups

Surface metallization of polyimide (PI) is the key process for the preparation of flexible printed circuit boards (FPCBs). To meet the miniaturization demand, the ultrathinness of FPCB by the removal of the intermediate adhesive layer is imperative. The common adhesiveless process relies on the surface activation of hydrophobic PI through alkaline hydrolysis to generate the hydrophilic carboxylate anion sites for the metallic deposition. However, the alkaline hydrolysis process involves the imide ring cleavage caused by the attack of a strong nucleophile (OH^-), resulting in mechanical destruction and surface coarseness of PI. In this study, a new PI is synthesized with the grafting of carboxylic acid groups as the active sites to intrinsically activate PI for efficient metallization. The surface activation is accomplished through an acid-base neutralization reaction in a dilute alkaline environment, which can suppress the alkaline hydrolysis reaction. The attenuated total reflection Fourier transform infrared spectroscopy analysis confirms a significant reduction of the extent of the imide ring cleavage in the carboxylic acid-grafted PI films. According to the microstructural examination using transmission electron microscopy, the deposited metal film adheres firmly to the carboxylic acid-grafted PI films through an interlocking effect of a broccoli bud-shaped nanocluster layer.

High-Performance and Simply-Synthesized Ladder-Like Structured Methacrylate Siloxane Hybrid Material for Flexible Hard Coating

A high performance ladder-like structured methacrylate siloxane hybrid material (LMSH) was fabricated via simple hydrolytic sol⁻gel reaction, followed by free-radical polymerization. A structurally ordered siloxane backbone, the ladder-like structure, which is an essential factor for high performance, could be achieved by a short period of sol⁻gel reaction in only 4 h. This results in superior optical (Transmittance > 90% at 550 nm), thermal (T5 wt % decomposition > 400 ℃ ), mechanical properties(elastic recovery = 0.86, hardness = 0.6 GPa) compared to the random- and even commercialized cage-structured silsesquioxane, which also has ordered structure. It was investigated that the fabricated ladder-like structured MSH showed the highest overall density of organic/inorganic co-networks that are originated from highly ordered siloxane network, along with high conversion rate of polymerizable methacrylate groups. Our findings suggest a potential of the ladder-like structured MSH as a powerful alternative for the methacrylate polysilsesquioxane, which can be applied to thermally stable and flexible optical coatings, even with an easier and simpler preparation process.