A comparative study of stress-based and fracture mechanics-based finite element simulation approaches for RDL based wafer level package

Conventional stress analysis (CSA) and fracture mechanics using cohesive zone modelling (CZM) approaches are currently available in the finite element analysis framework for virtual design evaluation of microelectronic packages. CSA exists for a long time and the CZM is currently being adopted widely, especially by the universities and R&D institutes. Both the approaches have their own advantages and challenges. In this scenario, a comparison of relative merits and limitations need to be evaluated to make efficient use of both the approaches in the package development process. Such a comparison aids the simulation engineers to gage the requirements of each approach and plan an affordable simulation strategy while maximizing the output. In this study we present a comparative evaluation of CSA approach and fracture mechanics approach using CZM for design evaluation of a simple fan-out wafer level package. We show the requirements (mechanical properties and mechanical and fracture strength details of materials) and merits (prediction capabilities) of both the approaches and thus gauge their viability and suitability for different design stages. We also show the specific advantages and challenges of CZM approach. We conclude that the CZM method enhances the virtual product development process through its capability of predicting the likeliness of delamination and damage. However, this approach has the prerequisite of fracture properties of the material interfaces. The initial (conceptual/preliminary) development phases of a new package require evaluation of a large number of candidate materials, processes and designs and the fracture strength (interface/bulk) data for all the material/process combinations are seldom available. The CSA approach is more suitable for such situation to narrow down the product parameters by comparative analysis. The candidate designs thus narrowed down can be simulated using CZM approach to evaluate the likeliness of delamination and modifications can be proposed to optimize them.