Numerical analyses of the competition between adhesive and cohesive fracture at a micro-patterned polymer-metal interface

All electronic devices contain microchips. A microchip contains many layers of different materials (Figure 1). During production, testing and usage, a percentage of the microchips fails because the material layers delaminate. This delamination can be reduced by roughening the interface between the materials. For roughened interfaces the delamination deflects in to the bulk material which is much tougher to fracture.

MSc student: Thijs Thurlings
Supervisors: Joris Remmers (TU/e), Olaf van der Sluis (TU/e & Philips)
Professor: Marc Geers
Associated company: Philips

The goal of this research is to determine the important material parameters that are responsible for the transition from interface to bulk fracture. Prior to this research experiments are preformed on a layered sample. A patterned roughness profile is used. The experiments showed both interface and bulk fracture (Figure 2).

A suitable method to reproduce the experiments in simulations is the Finite Element Method (FEM) with Cohesive Zones. The cohesive zones describes the energy dissipation due to the fracture by a traction separation law (TSL). A parameter study is preformed on the TSL's for the interface and bulk fracture. Important parameters of the TSL are the fracture toughness and the maximum normal and shear traction.

The normal to shear traction ratio of the interface TSL is the important material  parameter influencing the deflection behavior of the simulations (Figure 3).