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

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 um thick liquid mold layers were reliably blocking the oxidation.