Synthesis and Characterization of a Novel Quaternary Block Copolymerized Polyimide for Fan-out Wafer Level Package

Fan-Out Wafer Level Packaging (FOWLP) is considered to be one of the most important basic packaging forms for advanced packaging industry. Polyimide (PI), especially aromatic polyimide, stands out among many polymers due to its excellent comprehensive properties and has been used as a typical redistribution layer (RDL) dielectric material. However, the mismatch of coefficient of thermal expansion (CTE) between the polyimide (PI) insulating layer and copper wires in FOWLP always cause reliability issue. In this paper, one-pot method was used to synthesize block copolymerized PI (B-PI) and random copolymerized PI (R-PI) with the same ratio of the rigid segment and flexible segment, the two PIs were prepared by controlling the addition order of diamine and dianhydride. To better understand the relationship between their structures and properties, we also prepared R-PIs and B-PIs with different rigidity-flexibility ratios. These copolymers were characterized by fourier transform infrared (FT-IR), dynamic mechanical thermal analysis, thermomechanical analyzer and polarized light microscope. The test results showed that B-PI exhibits higher elongation at break and lower coefficient of thermal expansion than R-PI. In addition, the crystallinity and mechanical properties of B-PIs and R-PIs also changed regularly with the increase of the rigid segment ratio. The copolyimide films obtained by different feeding sequences exhibited excellent thermal stability, and the carbon residue rate at 800 °C was as high as 50 % or more. These results suggest their promising application as RDL dielectrics of FOWLP.