The Paradoxical Role of Sulphur in Molding Compounds: Influence on High Temperature Reliability of Cu-Al Wirebond Interconnects

This paper describes the role of sulphur on corrosion phenomena at the interface between the Cu ball and Al bondpad. Sulphur is usually linked to the adhesion promotor which is used to improve package robustness and second bond reliability, but can have other detrimental effects. A variety of techniques such as (in-situ) HTSL, chemical analysis of sulphur and performing a DOE with compound variants was used to demonstrate that the presence of significant levels of sulphur in the molding compounds can accelerate Cu-Al interfacial corrosion. The presence of a Pd coating on the wire retards this inter-metal corrosion but can lead to other chemical reactions at the side of the Cu ball.