Important factors for silane adhesion promoter efficacy: surface coverage, functionality and chain length

The effects of an ammonia-based catalyst, surface coverage, organofunctional group and chain length on silane adhesion promoter efficacy were examined at a benzocyclobutene (BCB)/silicon dioxide interface with silanes of varying functionality and chain length. Fracture-mechanics-based techniques, and X-ray photoelectron spectroscopy and contact-angle measurements were used to quantify the adhesion energy and silane surface coverage, respectively. Inclusion of a propylamine catalyst in silane solutions was found to affect both silane surface coverage and the resulting adhesion energy. However, in the absence of the catalyst comparable results were obtained with hydrolysis times in excess of 1 h. Only a weak dependence of adhesion energy on silane surface coverage was observed. After adhesion energy results for silanes with varying organofunctional group were normalized for differences in surface coverage, only the vinylfunctional silane was found to enhance adhesion of BCB to silicon dioxide, due to interaction of the vinylfunctional group with BCB during cure. A trend of increasing adhesion energy with increasing chain length was observed for CH3-terminated silanes (2 greater than or equal to n greater than or equal to 18), while an opposite trend of decreasing adhesion energy with increasing chain length was found for vinyl-terminated silanes (2 greater than or equal to n greater than or equal to 22). The results are compared to existing models of polymer chain entanglement.