Reduction of Leakage Current Along Polyimide Layers in Wafer Level Packaging

Abstract

Wafer level packaging (WLP) has become the backbone technology for chip-scale packaging and 3D integration used in compact, light-weight, and multifunctional electronic systems. Metal redistribution lines (RDL) and insulating polymer layers are the core constituents of WLP and the lateral leakage current between close-spaced RDLs have been a major concern for the electrical reliability in a dense package. In this article, it is demonstrated that Ar plasma related polyimide (PI) damage is the main cause of leakage current rather than metal residue from the RDL wet etch on the polymer surface. Through the optimization of the etch conditions after the PI descumming process by lowering RF power and raising ICP power for plasma, the leakage current of 1.6 μA is reduced to less than 5 nA. Furthermore, a model is proposed to explain the current conduction along the damaged PI layers. The results will be applicable to the fabrication of electronic devices and circuits on plastic substrate utilizing plasma-assisted processes.