Finite element thermomechanical analysis of electronic packaging problems using disturbed state constitutive models.

Abstract

In this dissertation a finite element procedure using the Disturbed State Concept constitutive models is proposed for the thermomechanical analysis of electronics packaging problems. First, microelectronics packaging types and the problems facing the electronics industry are discussed. Next, the literature in the field of constitutive models and the finite element procedures available for microelectronics packaging materials and interfaces is reviewed. The previous formulation of the Disturbed State Concept is modified so that different stresses and different strains are allowed in the intact and the fully adjusted parts of the material. Furthermore, the thermo elasto-viscoplastic with disturbance constitutive model is improved to handle the continuous temperature change and the hold time. These last features enhance the model so that it can be used in a finite element code to simulate the behavior of the microelectronics packaging materials and interfaces in temperature cycling. A new finite element procedure is developed to implement the improved Disturbed State Concept formulation. The finite element procedure includes a wide range of material models, starting from the linear elastic to thermo elasto-viscoplastic with disturbance. In order to eliminate the finite element mesh sensitivity encountered in strain-softening materials, a new procedure is proposed. The Disturbed State Average Strain method reduces or eliminates the finite element mesh sensitivity. This is proved through a number of example problems. The proposed finite element procedure is verified against a number of sets of experimental data obtained from the literature.