High frequency signal performance of PDMS based pressure conductive rubber with core-shell onion-like carbon-Ni fillers

The development of pressure conductive rubber (PCR) with enhanced high-frequency performance is crucial for semiconductor testing interfaces. In this study, core shell onion-like carbon‑nickel (CNi) particles were synthesized via a hydrothermal process, systematically optimizing six key parameters to improve bonding interactions with metallic nickel. Functionalization of onion-like carbon (OLC) was confirmed by Fourier Transform Infrared (FTIR) analysis, demonstrating successful carboxyl (-COOH) surface modification, which facilitated thiol exchange reactions. Experimental results showed that insufficient acid treatment times led to incomplete core-shell structures, while excessive reaction temperatures induced sulfur crystallization, hindering coating uniformity. By refining synthesis conditions—including a 6-hour acid treatment, a reaction temperature of 130 °C, and a 72-hour reaction time—uniform CNi coatings with an average thickness of 450 nm were achieved, as validated by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) analyses. The influence of magnetic field strengths (0.7 T, 1.0 T, and 1.3 T) and magnetization durations (3 and 6 h) on particle alignment within a Polydimethylsiloxane (PDMS) matrix was investigated. The highest surface area packing factor (22.8 %) was observed under a 1.0 T field for 6 h, while saturation effects limited further improvement at 1.3 T. Insertion loss measurements revealed that the CNi:Ni ratio strongly influenced electromagnetic performance. The 1:1 ratio exhibited the widest bandwidth (−3 dB at 471.84 MHz) and the highest material density, suggesting an optimal balance between conductivity and dielectric properties. These findings demonstrate the potential of CNi-Ni composites for tunable microwave devices and high-speed semiconductor testing applications.