Reliability Investigations of Polymer Based Redistribution Layers (RDL) Protected by a Mold Layer

Abstract

In this study, we demonstrate that a mold layer can protect a polymer-based redistribution layer (RDL) technology from copper oxidation. Copper oxidation occurs at high temperature in presence of oxygen, resulting in the growth of a copper oxide layer at the copper/polymer interface ultimately leading to reliability issues. Most commercial polymers used as dielectrics in polymer-based RDL technologies cannot prevent copper oxidation. Additionally, moisture permeating through the polymer accelerates the oxidation process. Therefore, mold layers, considered as a simple capping solution in RDL technologies were submitted to reliability stressing. It is found that granular mold layers cannot prevent copper oxidation regardless of their thickness whereas 200 mu m thick liquid mold layers were reliably blocking the oxidation.