Underfill adhesion to BCB (Cyclotene(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 betw een 69-90 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 402 2 and 4024 (with AP3000 adhesion promoter) and underfillers FP 4511 and 452 7 we find the die shear strength decreases an average of 11% for the four c omparisons. Adhesion promoters based on vinyltriacetoxysilane or 3-aminopropyltriethoxy silane show equivalent die shear performance. Substrate surface cleaning ba sed on UV ozone treatment reveals oxidation of the BCB surface which by SIM S analysis remains <0.1 mu m deep after 10 min of treatment.