Cu-adherent poly(ether ether ketone) with low dielectric loss via self UV-initiated surface modification for high frequency application

With the rapid advancement of 5G communication technologies, there is an urgent need to develop materials with low dielectric loss for compact and high-efficiency flexible copper clad laminates (FCCL). To address the issue of relatively high dielectric loss of the combination of a polyimide (PI) film and a bonding sheet for 5G FCCL substrate, this study investigated poly(glycidyl methacrylate)-grafted poly(ether ether ketone) (PEEK-g-PGMA), which was prepared via UV-induced self-initiated surface polymerization. The visual appearance and mechanical properties of the PEEK were maintained after the grafting process, and the thin PGMA layer was characterized using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and contact angle measurements. To optimize the processes of PGMA grafting and hot pressing, 90° peel tests were conducted. As a result, the optimized grafting and hot-press conditions were found to be UV irradiation of 4 min, 1.0 M monomer solution, and hot pressing at 180 °C for 60 min. At 28 GHz, the PEEK-g-PGMA exhibited lower dielectric constant and loss than those of the PI films with commercial bonding sheet. The study presents a straightforward approach to prepare the PEEK-g-PGMA films as a potential bonding sheet-free substrate for 5G FCCL.