Transition Metal β-diketonate Adhesion Promoters in Epoxy-Anhydride Resin.

Epoxy to copper adhesion has occupied the center stage of electronic packaging to support the reliability of numerous novel structures. Compared to substrate pre-treatment, processing and cost considerations are greatly in favor of adhesion promoters in epoxy formulations to achieve exceptional adhesion and moisture resistance. In this paper, we present series of coordination compounds: first row transition metal β-diketonates to perform such function when added in epoxy/anhydride resins. The over 30% (before moisture aging) and 50% (after moisture aging) enhancement in lap shear strength were found using the champion metal chelates, notably Co(II) and Ni(II) hexafluoroacetylacetonate (6Facac 2 ), where interesting metal and ligand dependence on the adhesion properties were also observed. From extensive surface bond composition analyses on the adhesively failed samples using X-ray Photoelectron Spectroscopy (XPS), we found that the increased population of oxygen containing functional groups, especially esters, are fundamental for the adhesion improvement. Assisted by XPS depth profile on the fractured epoxy side and in-situ Fourier-transform Infrared Spectroscopy (FTIR) tracking epoxy-anhydride curing, our previously discovered latent cure performances of the metal chelate additives through interacting with phosphine catalysts were regarded pivotal for pacing anhydride and acid intermediate consumption, which is necessary for the very localized interfacial esterification reactions to occur and provide abundant covalent bonding between the adhesive and the adherend. Further examinations on the XPS binding energy of polar functional groups, as well as contact angle and dielectric spectroscopy of the doped epoxy also revealed metal-polymer (and interfacial bonding) coordination that contributed to the adhesion and moisture resistance properties. These findings demonstrate the use of transition metal complexes as promising adhesion promoters in epoxy resins, and the mechanisms discussed here should be helpful in stimulating future design of functional additives pursuing both cure kinetics control and polar group coordination ideas for more robust epoxy-Cu joints. This article is protected by copyright. All rights reserved.