Thermomechanical analysis in electronic packaging with unified constitutive model for materials and joints

A unified constitutive modeling approach based on the disturbed state concept (DSC) provides improved characterization of thermomechanical response of joining (solders), ceramics and printed wire board (PWB) materials in electronic packaging. Various versions in the DSC approach are calibrated and validated with respect to laboratory test data, and are implemented in a nonlinear finite element (FE) procedure. The hierarchical nature of this procedure permits the user to choose a constitutive model, simple (elastic) to sophisticated (elastovisco-plastic with disturbance), depending upon the material and need. The FE is used to analyze thermomechanical behavior of two typical problems: (1) leadless ceramic chip carrier (LCCC) package; (2) solder ball connect (SBC) package. The FE results under cyclic thermal loading are compared with experimental data for the two packages, and with a previous FE analysis for the SBC package. In conjunction with the idea of critical disturbance at which thermal fatigue failure can occur, the analyzes allow identification of cycles to failure, N/sub f/, and evaluation of reliability of the package. In the case of the SBC package, the analysis permits an evaluation of ball spacing on the thermomechanical behavior. The DSC approach can provide an integrated and improved procedure compared to available models for elastic, plastic, creep strains, and microcracking leading to degradation of strength and fatigue failure for a wide range of problems in electronic packaging under thermomechanical loading.