Surface composite engineering of polyimide to create amine functionalities for autocatalytic metallization

Highlights: • Surface composite engineering of PI is accomplished by covalent bonding of aminosilane. • Aminosilane is an efficient molecular adhesive for Cu/PI heterogeneous junction. • Aminosilane with one amine unit performs better with good adhesion strength. • Molecular conformation of aminosilane/PI bonding is studied theoretically. Autocatalytic metallization of polyimide (PI) is accomplished through surface composite engineering as a facile approach to fabricate flexible printed circuit boards. The surface composite engineering of PI involves the generation of active sites by plasma activation, attachment of amine-terminated organosilanes through covalent bonding with the active sites, adsorption of a palladium catalyst by a complex reaction with the amine groups, and electroless deposition of copper through autocatalytic metallization. Three aminosilanes with various numbers of amine units are employed to silanize the PI surface and to create amine functionalities, successfully achieving a high coverage of copper deposition. The standard 90° peeling test further identifies that the aminosilane with one amine unit outperforms the others with two and three amine units in the adhesion performance of the copper layer, with the highest peel strength reaching 0.8 kgf/cm. A systematic study is performed to experimentally and theoretically explore the grafting conformation of the three aminosilane/PI composite systems at the atomic level, and the correlation with the peel strength performance is also investigated.