Corrosion Mechanisms of Copper and Gold Ball Bonds in Semiconductor Packages: A Unification of Structure-Based Inference and Electrochemical Investigation

Abstract

Ball bonding is the most widely used interconnection method in microelectronic packages. It has enabled many modern technologies including medical implants, aerospace, automobiles and Internet of Things. In the automotive industry, driving automation and advanced driver assistance systems motivated mainly by safety enhancement are gaining traction. The reliabilities of these technologies necessitate those of the underlying ball bonds. This chapter provides interpretation of the mechanisms of corrosion that causes reliability failures of Cu and Au ball bonds, by unifying approaches based on microstructure characterization and electrochemical investigation. The corrosion of Cu ball bonds starts with pitting of the most Curich layer (MCRL) under the chlorinated water layer, evolves into crevice corrosion, and can be assisted by stress corrosion cracking. In the MCRL, Al is preferentially oxidized, while the Cu atoms remain largely immune and coalesce to form nanoparticles. Four methods to address the corrosion are presented. Limited data indicate the same corrosion mechanisms for Au ball bonds.