An assembly process oriented thermal-mechanical characterization of a fan-out wafer-level package

This study focuses on the stress analysis using finite element methods regarding a wafer-level Cu pillar package assembly process. The detailed assembly process is described, and a process-oriented thermal-mechanical coupled model is developed as the stress analysis tool. The finite element analysis is divided into two sections, namely the identification of the critical assembly step, and the analysis of the critical stress development. The package dimension and material property variables are parametrized by taking all the possibilities that could happen in the assembly process into consideration. The influence of each parameter is characterized and critical parameters are addressed, together with some initial assembly test results taken as validations. It is found that the most critical step for the solder is the reflow process, and the most critical stresses are the Cu pillar solder shear stress as well as the solder ball tensile stress.