Adhesion enhancement between colorless biphenyl polyimide copolymerized film and magnetron sputtering Cu for FPC circuit board

Polyimide (PI) film is one of the world's leading thin film insulation materials, which can be used in electronic applications in the aerospace, medical, and automotive industries. Colorless polyimide (CPI) has significant advantages in the field of flexible printed circuit (FPC) board as substrate materials. As the substrate material for circuit boards, the bonding strength between polymer films and metals is crucial. The peel strengths of CPI films were analyzed as an important parameter for evaluating FPC boards. The films exhibited good light transmittance and thermal performance. Diamine monomers with amide bonds and biphenyl structures in the main polymer chains were synthesized to improve peel strength and transparency. The diamine monomers (AB-TFMB and 6FAPTA) were prepared through a series of experiments involving acyl chloride/amino group condensation and nitro group reduction. The CPI films were prepared through the chemical imidization method, achieving a thermal weight loss (5%) at 462.47 °C, average peeling force of up to 3.104 N, and good light transmittance of up to 89.8%. Finally, after conducting 100 000 folding tests, the CPI films displayed excellent mechanical properties, with no cracks observed in the surrounding buffer layer. This research could provide important insights for developing new substrate materials for FPC boards.