Underfill adhesion to BCB (Cyclotene/sup TM/) bumping and redistribution dielectrics

The adhesion of several commercial underfills (Dexter Hysol FP4511, FP4527, and CNB775-34) to BCB (CYCLOTENE 4022, 4024) has been studied through die shear testing and subsequent failure analysis. Die shear values range between 69-30 MPa. Failure analysis by optical microscopy, profilometry and XPS spectroscopy indicates mixed mode failure at various interfaces. From the die shear data collected before and after 24 h water boil for Cyclotene 4022 and 4024 (with AP3000 adhesion promoter) and underfillers FP 4511 and 4527 we find the die shear strength decreases an average of 11% for the four comparisons. Adhesion promoters based on vinyltriacetoxysilane or 3-amino-propyltriethoxysilane show equivalent die shear performance. Substrate surface cleaning based on UV ozone treatment reveals oxidation of the BCB surface which by SIMS analysis remains <0.1 /spl mu/m deep after 10 min of treatment.