Understanding Protective Overcoat Damages: Failure Analysis to the Next Level

Failure analysis (FA) is key in root cause identification for any problem solving journey. Diagnosis given provides insights on mechanisms by which failures occur. This helps in determining factors that lead to the failure and consequently the root cause, thus easier to provide corrective actions. In mid June 2004, a sudden increase in test fall-outs was encountered. Several devices from different product groups were affected. Fail modes reported were supply shorts and functional fails. FA on rejects showed PO damages with burnt metals as the physical defect of the rejects. PO damages are commonly induced mechanically. Burnt metals, on the other hand, are usually identified with electrical overstress (EOS) or electro-static discharge (ESD) related event. Both features were observed on inspected rejects; hence root-cause identification became a challenge. Conflicting views from counterparts added to the confusion. Experts in the US leaned on the EOS or ESD side of the case while counterparts in France maintained the mechanical angle of the issue. These conflicting inputs brought about different insights on different mechanisms leading to PO damages