Micromechanical modeling of stress evolution induced during cure in a particle-filled electronic packaging polymer

Particle-filled polymers are widely used in electronic industries. From microscale view, cure-induced residual stress can be generated not only by the external constraints but also by the constraint effect among the particles. In this paper, a three-dimensional micromechanical finite element method (FEM) model has been setup for a silica particle filled epoxy. In the micromechanical model, the epoxy matrix is modeled with a previously developed cure-dependent viscoelastic constitutive model, whereas the silica particles are modeled as elastic with high stiffness. Cure shrinkage is applied to the matrix as an initial strain for each time increment. The cure-dependent viscoelastic properties were obtained from shear and tension-compression dynamical mechanical analysis measurements. Cure shrinkage and reaction kinetics were characterized with online density measurement and differential scanning calorimeter measurements, respectively. In order to simulate a partly constrained object, the micromechanical model is coupled with a macromodel FEM analysis. The displacements from the macromodel are used as boundary conditions for the micromodel. The effect of external constraints on the generation of the micro stresses is studied by using the boundary conditions related to different external constrained states.