Assessing the NSOP (non stick on pad) bond pad by EDX, XPS and ToFSIMS analysis

NSOP defect is a common defect faced by IC packaging assembly house. The failure modes normally happen when the wire bond process is not able to bond the wire ball head on the silicon chip bond pad surface. In this analysis, the localized NSOP defect had been observed with the gold wire bonding process on gold bond pad itself. Preliminary surface analysis inspections by FESEM and EDX have been done and confirmed that the NSOP failure is cannot rule out is related to contamination issues or process. However, with the FESEM / EDX analytical tool, the real root cause of the NSOP defect still remains unresolved due to no differences in the results between the defect pad and good pad. To deeply understand the NSOP phenomena, surface sensitive analytical tools such as XPS and ToFSIMS have been applied in this analysis. XPS preliminary results finding showed that the NSOP defect is highly suspected due to the plasma cleaning process inducing bond pad surface polarity change and contributing to absorption / re-deposition of contaminate from surrounding. To further strengthen the hypothesis as mentioned, ToFSIMS analysis has also been carried out to prove the finding as observed from XPS analysis.