The competition between adhesive and cohesive fracture at a micro-patterned polymer-metal interface

It is common practice for polymer-metal interfaces, frequently encountered in microelectronic devices, to improve adhesion by surface roughening or micro-patterning. The competition between adhesive fracture and cohesive fracture in the vicinity of a patterned interface, i.e., interface crack deflection, is one of these key mechanisms that contribute significantly to the macroscopic adhesion. In this paper, these fracture phenomena are described simultaneously by cohesive zone elements with an exponential traction-separation law (TSL) for the adhesive failure and an initially rigid, exponentially decaying, TSL for the cohesive failure. It is demonstrated that the conditions at which crack kinking occurs are dominated by fracture strength values as opposed to the commonly used fracture toughness values. Experimental verification is performed by means of four point bending tests on specifically designed micro-patterned polymer-metal samples.