The effect of NaOH on metal/polyimide adhesion

Via generation is one of the important processing steps that must be performed in the fabrication of Multichip Modules (MCM). Vias generated by wet chemical etching using strong bases Like NaOH and KOH can lead to increased reliability in performance. A significant amount of sodium was detected by ESCA on PMDA-ODA polyimide etched in NaOH, rinsed in deionized water and neutralized with sulfuric and acetic acids. The adhesion of metal to the caustic treated polyimide was poor. Fracture was not at the metal/polymer interface but in the polyimide below the interface. The fracture polyimide surface was rich in sodium. The adhesion of metal to the polyimide improved with acid neutralization and heat treatment.