A wet process for forming an adhesive copper layer on polyimide film

A wet process for forming an adhesive Cu layer on polyimide (PI) film was developed. In this process, the surface of the PI film is pretreated in plasma, followed by the formation of a ligand-bearing organic layer of 3-aminopropyl-triethoxy silane (APTES) molecules. After catalyzation with a solution containing Pd ions, thin layers of NiB as the underlayer and that of Cu as the conductive layer are deposited by electroless depositions, and then a 10 μm thick Cu layer is electrodeposited. The peel strength of the specimen prepared by this method was found to depend on the morphology of the NiB underlayer. A continuous NiB layer functions as a barrier layer that prevents Cu from contacting the PI film. In the presence of this efficient barrier layer, the peel strength was found to improve after annealing at 150°C.