High-performance black polyimide with improved solubility for flexible printed circuit boards.

With growing attention to the protection of circuit design, the demand of black polyimide (BPI) for flexible printed circuit board (FPCB) is increasing. However, the existing BPIs suffer from problems of poor mechanical and electrical properties, low solubility and masking capacity. To address these issues, a diamine monomer (TPCPODA) containing tetraphenylcyclopentadienone (TPCP) connected with phenyl ether unit was designed and prepared, which was subsequently reacted with 4,4'-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) to prepare a soluble intrinsic BPI (TPCPOPI). TPCP grafted with phenyl ether acts as chromophores that shift the absorption scope of PI to the long wave direction. The resulted TPCPOPI shows a cut-off wavelength (λ_cut) high to 673 nm. Theoretical calculations suggest that the visible absorption of TPCPOPI is mostly resulted from the electrons transitions of HOMO to LUMO within diamines moiety, in which the charges chiefly migrate from the aryl units at 2, 5-position to cyclopentadienone. Moreover, TPCPOPI shows outstanding electrical, mechanical and thermal properties and excellent solubility. Further investigation shows that the TPCPOPI-based two-layer flexible copper clad laminates (2L-FCCLs) has high peeling strength due to the incorporation of ketone and ether units. This work offers a prospective solution for the property improvement of BPIs for FPCBs. [ABSTRACT FROM AUTHOR]