Low-temperature bonding of surface-activated polyimide to Cu Foil in Pt-catalyzed formic acid atmosphere

In this study, a two-step process involving oxygen plasma surface activation and thermos-compression in Pt-catalyzed formic acid gas was used to bond Cu foil and polyimide. The oxygen plasma was used to activate the polyimide surface to achieve strong adhesion with sputtered deposition film, and the Pt-catalyzed formic acid gas removed the oxides on the Cu surface effectively to promote bonding between Cu foil and polyimide. Via this method, a void-less bonding with a maximum shear strength of 20.31 MPa was achieved. The plasma bombardment was found to promote the formation of C-O-Cr and N-Cr bonds between polyimide and deposition metals, which improved their adhesion. After shear test, striped metal films remained on fracture surfaces at both polyimide and Cu foil sides, suggesting the fracture mainly occurred within adhered deposition metals rather than at bonding interface. This low-temperature bonding method is promising to achieve the direct integration between polyimide and copper foil without adhesive, which plays a key role in flexible device integration.