Influence of rigidity and flexibility of polyimide segment on the adhesion between polyimide and copper

Polyimide (PI) is widely used in aerospace, military and microelectronics due to its excellent comprehensive performance. With the development of 5G high-frequency communication technology, PI occupies an important position in redistribution layer (RDL) in fan-out wafer-level packaging (FOWLP). Thereinto, the stable bond and high adhesion between PI and Cu wire is one of the decisive factors for the reliability of RDL in FOWLP. In order to improve the adhesion between PI and Cu, in this study, diamines with benzimidazole structures 2-(4-aminophenyl)-3H-benzimidazol-5-amine, (APBI) and siloxane structures 1,3-Bis(3-aminopropyl) tetramethyldisiloxane, (BATMS) were introduced to PI as adhesion-promoting components. At the same time, 4,4'-Oxydiphthalic anhydride (ODPA) with flexible ether linkage and 1,2,4,5-Benzenetetracarboxylic (PMDA) with rigid structure were added to control the flexibility so as to study the influence on the adhesion with Cu. The 90° peel force between PI and Cu film was tested after PAA was spin-coated on Cu film and cured at 350°C under nitrogen atmosphere. The results show that the peel force between PI and Cu reaches a maximum value of 1.95 N/3mm when the ratio of ODPA and PMDA is 3:7. The introduction of ether bonds also enhanced the mechanical properties and thermal resistance of FPIs. The elongation at break of FPI increased to 11.3%, and the tensile strength increased to 143.23MPa. The introduction of ether linkages increased T d,5% and T d,10% to 493°C and 559°C. In conclusion, by tuning the flexibility of the monomers, PIs with high Cu adhesion were obtained. The synthesized PI has good comprehensive properties and is expected to be applied to FOWLP.