A Novel Method for PBO Adhesion Characterization in WLCSP Package

This paper introduced a novel micro pillar structure for Polybenzoxazoles (PBO) adhesion test. The adhesion strength of PBO to silicon nitride, PBO to plated copper and PBO to PBO was studied under different curing temperature. Nano indentation test was performed and Focused Ion Beam (FIB) was done to verify the failure mechanism. We observed that the adhesion strength of PBO to plated copper is weaker than that of PBO to silicon nitride and PBO to PBO. Optimizing curing temperature can improve PBO adhesion to silicon nitride and plated copper. This study provides a method to compare the adhesion of relevant PBO interfaces. The analysis results can provide a guideline for design and process improvement for Wafer Level Chip Scale Package (WLCSP).