Comparative studies of green molding compounds for the encapsulation of Cu/low-k packages

The experimental results are reported on the 80 leads ETQFP module-level understanding of the performance between two green molding compound types in the packaging of 90nm Cu/low-k Si devices using Cu/Ag leadframe. The stress-induced Cu/Ag leadframe-finish migration is observed for a P-contained molding compound, while a new hydrophobic nitrogen-based flame retardant molding compound does not lead to any electromigration failure. Based on the extensive electrochemical and failure analyses, the failure mechanism is elucidated: it is found that Cu/Ag lead-finish migration is induced by the stressed formation of phosphoric acids during extended biased and specific temperature/moisture stressing. Its dendritic extension reflects a non-coplanar pattern and a cathodic-anodic electrochemical cell characteristic through the epoxy matrix. A migration model was proposed to prevent similar failure recurrences in future materials introduced to the industry.