Characterization of polymer/epoxy buried interfaces with silane adhesion promoters before and after hygrothermal aging for the elucidation of molecular level details relevant to adhesion

Abstract

Buried interfacial structures containing epoxy underfills are incredibly important in the microelectronics industry and their structures determine the interfacial adhesion properties and ultimately their lifetime. Delamination at such interfaces leads to premature failure of microelectronic devices. In this work, the intrinsically surface sensitive technique, sum frequency generation (SFG) vibrational spectroscopy, was utilized to investigate the molecular structure of buried epoxy interfaces before and after accelerated stress testing in order to relate the molecular-level structural changes to the macroscopic adhesion strength and determine what effect silane adhesion promoters have on polymer/epoxy systems. Strongly hydrogen bonded water was detected at hydrophilic epoxy interfaces and this was correlated with a large decrease in adhesion strength. The addition of a small amount of adhesion promoters drastically improved the adhesion strength following accelerated stress testing at a relatively hydrophilic polymer/epoxy interface, and they were also capable of preventing interfacial water. A hydrophobic polymer/epoxy interface was also studied and silane adhesion promoters were found to improve the adhesion strength following stress testing of the hydrophobic interface as well. This research demonstrates that molecular structural studies of buried epoxy interfaces during hygrothermal aging using SFG vibrational spectroscopy can greatly contribute to the overall understanding of moisture-induced failure mechanisms of organic adhesives found in microelectronic packaging.