Moisture-assisted subcritical debonding of a polymer/metal interface

Abstract

Subcritical debonding of polymer/metal interfaces has important implications for the reliability of a range of modern device technologies containing thin layered structures, although the physics of the underlying crack-growth mechanisms are not well understood. This study investigates the effect of moisture on subcritical debonding at the interface between a silica-filled epoxy resin and a copper substrate electroplated with a nickel layer. Subcritical debond-growth rates in the range of 10−5 to 10−11 m/s were characterized as a function of the applied strain energy release rate, GA. Particular attention was given to the relationship between the debond tip strain energy release rate, Gtip, and the measured debond growth rates. The kinetics of interfacial debond growth were rationalized in terms of a stress-dependent chemical reaction and mass transport of the environmental species to the debond tip. The order of the chemical reaction with respect to water was determined and found to be surprisingly high (n∼5). In the transport-controlled region, the rate of debond growth was found to increase linearly with the partial pressure of water vapor. The effects of salient interface parameters including the peak stress in a cohesive zone used to model the fracture mechanism were explored.

Crack growth in structural adhesive joints in aqueous environments

“…It should be noted that previous researchers [8][9][10][11][12][13][14] have also reported results from studies on the sub-critical crack growth in epoxy-bonded joints which follow the general pattern reported by Wiederhorn [7].…”

Critical and Subcritical Adhesion Measurements of a Model Epoxy Coating Exposed to Moisture Using the Shaft-Loaded Blister Test

“…Therefore, subcritical adhesion testing simulates the failure occurring in the real-life application or service life of the adhesive. Crack growth can be driven by small applied loads generated by residual stresses, thermomechanical cycling, and mechanical or vibrational loading during service [13]. An additional advantage of subcritical testing over conventional adhesion tests is the reduced ambiguity associated with the dependence on crack velocity on the measured adhesion energy, which is associated with viscoelastic effects at the crack tip and in the bulk adhesive.…”

“…A schematic of a typical v-G curve is shown in Figure 1. Three regions are usually observed, which are related to the mechanism for crack advancement [13][14][15]. Region III is associated with critical fracture events, which is independent of the environment for bulk glass fracture.…”

Crack propagation along polymer/non-polymer interfaces

“…The change in crack front geometry can be understood invoking the physical picture of crack growth as a stress aided thermally activated process (subcritical crack growth) along an interface. Adopting for simplicity an Arrhenius description of the average dynamics of the crack movement (other formulations are possible, see [1]) and therefore disregarding the distinction between initiation of bursts at the crack front and propagation of already existing bursts, one can write:…”