Advantage and current limitations of advanced fracture mechanics for 3D-integration and BEoL under CPI aspects
Abstract
The ongoing development towards increasing functional density and performance drives the improvement of IC packaging and interconnection technologies. However, new integration technologies, such as through silicon vias (TSVs) for 3D stacking for heterogeneous systems as well as rigid micro-bumps together with the utilization of delicate new (porous ultra low-k) materials weaken the mechanical stability. As a result, the risks of cracking or delaminations increase e.g. in back-end-of-line (BEOL) structures or in the surrounding of TSVs. Chip package interaction (CPI) under thermal loading, assembly loading as well as residual stresses from different processing steps provide the dominating thermo-mechanical stress situations. In this field, qualified Finite Element Modeling (FEM) techniques play a well accepted key role to manage damage, cracking and delamination risks in the package design phase and also during failure tolerance optimization. Well defined/measured materials properties, loadings, boundary conditions and residual stresses from manufacturing are preconditions to ensure the quality of simulation results. Unfortunately, stress/strain singularities at certain locations within the designs under investigation call for advanced approaches taking into account the stress singularities, i.e., fracture mechanics approaches, instead. The contribution explains classic fracture mechanics approaches for bulk fracture and material interface delamination investigations as well as their recently realized extensions and current limitations. In contrast, advanced approaches allowing the simulation of crack initiation and propagation like cohesive zone modeling (CZM) and extended FEM (X-FEM) will be explained and discussed with respect to their advantages/disadvantages. Their benefits for the thermo-mechanical reliability optimization will be explained with the aid of 3D IC-integration, TSV and a smart lighting assembly, in detail.
