Modelling thermomechanical degradation of moulded electronic packages using physics-based digital twin

Abstract

Semiconductor devices are commonly encapsulated with Epoxy-based Moulding Compounds (EMC) to form an electronic package. EMC typically occupies a large volume within a package, and thus, governs its thermomechanical behaviour. When exposed to high temperatures (150°C and above), electronic packages predominantly show oxidation of the outer layer of EMC. Oxidized EMC exhibits notably different material properties, resulting in a modified deformation pattern of a thermally aged package under varying thermal loads. As the oxidation layer grows in thickness, its mechanical properties also evolve, indicating distinct phases of the oxidized material at different stages of thermal ageing. Reflecting these changes (i.e., the current state of degradation) into a Finite Element (FE) model-based analysis can provide better insights into failure prediction and component reliability. It requires updating the geometry and material behaviour as a function of ageing. This paper presents a systematic procedure to build a continuously updated physics-based Digital Twin of a thermally aged flip-chip package that can represent intermediate oxidation stages. First, experimental measurements are carried out to quantify the growth of the oxidation thickness at 150°C and a diffusion-dominant mathematical model is proposed. Then, an accurate geometry of the test package is prepared with a parametric outer layer from all exposed sides of EMC to represent the oxidized layer at different stages of thermal ageing. Next, the experimental characterization of a few partially oxidized EMC specimens is done, and analytical methods are utilized to extract the thermomechanical properties of the oxidized EMC at different stages of ageing. Experimental warpage data of aged test packages are utilized to verify the defined material-model parameters that represent curing shrinkage, thermal expansion, glass transition, and corresponding elasticity moduli of the oxidized EMC at select stages of ageing. Then, a workflow to establish continuity in the material model is presented. Finally, the developed Digital Twin is utilized for an FE analysis to study the change in the trend of out-of-plane package deformations as a function of several stages of EMC oxidation.