Moisture and temperature effects on the reliability of interfacial adhesion of a polymer/metal interface

Although moisture can considerably alter the mechanical performance and the overall reliability of microelectronic assemblies, the interfacial and material constitutive damage behavior from moisture is not entirely understood. In this paper, the effect of moisture content on the interfacial adhesion of an epoxy based underfill adhesive with a copper alloy substrate is studied. Test specimens were divided into five test groups and subjected to four different levels of moisture preconditioning. The test groups included fully dry, 85°C only, 85°C/50%RH, 85°C/65%RH, and 85°C/85%RH, with the latter four test groups being exposed for a duration of 168 hours. Underfill flexural bend test specimens were used to measure the change in the underfill elastic modulus as a function of increasing moisture concentration, while underfill/copper bilayer test specimens with prefabricated interface cracks were used to measure the critical load of fracture of the interface as a function of interfacial moisture content. Both the critical load of fracture and underfill elastic modulus values were used to determine the interfacial fracture toughness of the underfill/copper interface for a particular level of moisture preconditioning. After fracture testing, the chemical composition of the interface was evaluated using X-ray Photoelectron Spectroscopy (XPS) to identify the role of oxide growth on the interfacial fracture toughness results. The results of this study provide the intrinsic behavior of the interfacial toughness as a function of increasing moisture concentration, and include the effects of oxidation, thermal aging, and elastic modulus variation with increasing moisture content after moisture preconditioning.