Process-induced residual stresses analysis in plastic-encapsulated integrated circuit packages

A methodology has been developed for numerical modeling to investigate warpages, residual stresses, and failures caused by thermal mismatch in plastic integrated circuits (IC) packages. In particular, this work focuses on the characterization of the material properties to realize thermo-mechanical behaviors numerically. Material models are developed from experimental data and used to simulate the mold filling process and to perform the thermo-mechanically-coupled viscoelastic finite element analyses.; The mold filling process is simulated with a control volume finite element method (CVFEM). This numerical simulation is used to study the mold filling process and to provide more realistic input values to evaluate the residual stresses. Once the package design, theological properties, and cure kinetics of an epoxy-molding compound and process conditions are specified, predictions of the melt front advancement, distributions of temperature, degree of cure, and other process-related output data can be calculated. The degrees of cure and temperature profiles of the package after mold filling process are predicted. The results are used as initial conditions in the viscoelastic finite element analysis to investigate the residual stress profiles and warpages.; A good understanding of the viscoelastic behavior of an epoxy-molding compound is essential to construct an accurate finite element analysis model. The experimental characterization should identify a viscoelastic behavior for the epoxy-molding compound. Thermo-mechanically coupled viscoelastic finite element analysis is used to estimate the residual stress profiles and the warpage during the cooling process. A 160-pin thin plastic quad flat package (TPQFP) assembly is chosen as a reference case. The finite element model simulates a very complex configuration with 160 pins. The model characterizes possible material failures as affected by the package configuration and die size. The simulation results are compared with measurements from piezoresistive stress chips and also compared with results obtained from the conventional elastic model.; A parametric study is done to investigate the relations between the residual stress and the material properties, and compare the residual stresses and the process conditions. This study will be used to optimize the process conditions and provide the optimized guidance for material selections.