Key Research Areas

Reliability of Interfaces

Delamination of two materials, e.g. epoxy-moulding compounds and the copper-lead frame, or a cohesive break due to an interface defect is common in microelectronic components. Interfaces are vulnerable for moisture diffusion, and stresses can be imposed by thermal mismatch or from moisture-induced swelling. If the reliability of a material is to be evaluated using simulation, e.g. finite element modelling, then in addition to the properties of the individual materials it is also necessary to determine the critical parameters at the interface. The Environmental & Reliability Engineering department uses a range of experimental methods for the characterisation of interfaces, including:

  • 3-point and 4-point bending with exposure to moisture and temperature variation:
    Classic methods for determining the energy release rate Gc in bimaterial samples
  • Mixed-mode bending with exposure to moisture and temperature variation::
    Methods to determine Gc depending on the load angle Y (proportion of tensile or shear force)
  • Advanced mixed-mode bending:
    Apparatus to determine Gc (Y) for package-sized samples over the full range with only a few measurement steps

In addition to the experimental investigations, simulations are evaluated and the interfaces are investigated using the following methods:

  • Virtual Crack-Closure Technique (VCCT ):
    Classic FEM evaluation algorithm for Gc(Y)
  • Cohesive Zone Modelling (CZM):
    Interface elements for FEM with fracture capabilities
  • Molecular dynamics simulations:
    Evaluation of thermodynamic interactions at the atomic level.