Modeling of separation behavior of epoxy/Cu interface using molecular dynamics simulation

Abstract

Epoxy molding compounds (EMC) have been widely used in electronic packaging industry as adhesives, for example, die-attach and underfill. However, interfaces between EMC and other components such as copper substrates are weak and prone to delamination, due to large interfacial stresses developed during thermal cycling processes. Cohesive zone finite element method is able to simulate fracture initiation and propagation along a prescribed path, thus is an ideal choice of interface performance evaluation. However, this continuum mechanics based method relies on the determination of a traction-separation law to define cohesive elements. To this end, molecular dynamics (MD) simulation is conducted in this work to extract traction-separation law from a fully-atomistic model for epoxy/Cu interface at finite temperature. The epoxy studied in this work is a novel epoxy molding compound synthesized by curing tri/tetrafunctionalized EPN1180 with Bisphenol-A. A fully atomistic model for epoxy reflecting its network nature was created by applying a cross-linking algorithm to a confined layer with 2D periodic boundary condition assigned, containing a physical mixture of monomers. The interface model was built by laying epoxy slab with 2D crosslinked network structure on Cu substrate, and further optimized by energy minimization and MD simulations. MD simulation of tensile deformation was then conducted to extract traction-separation law for epoxy/Cu interfaces. Failure of the interface model was found to initiate within epoxy, localized within an interfacial zone, but transit to complete interface separation in the end.