Novel polyimides with improved adhesion to smooth copper and low coefficient of thermal expansion

Polyimides (PIs) have been extensively developed as interlayer dielectrics in electronic package industry due to their excellent comprehensive properties. However, the insufficient adhesion between PI and copper wires usually led to delamination and thus compromising the reliability of applications. In this work, a diamine monomer (SPMNH2) that contained pyrimidine side groups and ether bonds was synthesized, and a series of its copolyimides (SPI) were prepared by copolycondensation with 2-(4-aminophenyl)-1H-benzimidazol-5-amine (APBI) and pyromellitic dianhydride (PMDA). The incorporation of pyrimidine rings, along with the presence of benzimidazole rings promoted the adhesion between PI and copper (1.3805 N/3 mm of SPI-4). In addition, a desired coefficient of thermal expansion (15.28 ppm/K of SPI-4) close to that of copper was obtained, facilitating the adhesion of the interface during high-temperature processes. Moreover, SPI-4 exhibited exceptional mechanical (the elongation at break of 44.02% and tensile strength of 191.64 MPa) and thermal properties (Tg = 363.70 °C, T5% = 519.33 °C). Therefore, the high-performance SPI films showed great potential in advanced packaging.