Disturbed state concept of materials and interfaces with applications in electronic packaging

Abstract

Although a number of idealized constitutive models have been proposed in the past, to include factors such as elastic, plastic and creep strains and microcracking and damage, no unified model has yet been developed to understand and model the behavior of materials and joints in semiconductor chip-subtrate systems and packaging. Such models are important to analyze and predict the response for design and reliability assessments of packaging problems. This dissertation presents formalization and use of the recently developed approach called the disturbed state concept (DSC) for the characterization of the thermo-mechanical behavior of materials and joints. It is a unified approach and allows hierarchical use of the model for factors such as elastic, plastic, and creep strains, microcracking (damage) and softening and stiffening. The DSC model is used here for a number of materials such as ceramics (e.g. Aluminum Nitride), silicon ribbon and silicon doped with oxygen. The joining materials considered are different solders (e.g. 60%Sn-40%Pb, 90%Pb-10%Sn, and 95%Pb-5%Sn). Particular attention is given to solders used in the IBM-604 PowerPC package; which is a ceramic ball grid array (CBGA). A number of mechanical and ultrasonic tests are performed under uniaxial tension and compression loading for aluminum nitride. Test data available from the literature is used for the solders, silicon ribbon and silicon doped with oxygen. The DSC model is calibrated with respect to the test data in which the material parameters are found and affected by factors such as stress, cyclic loading and temperature. Then the incremental constitutive equations are integrated to backpredict the observed behavior for the tests used in the calibration and independent tests not used in the calibration. Overall, the model provides satisfactory correlation with the observed behavior. A nonlinear finite element procedure with the DSC is used to analyze the CBGA package with emphasis on the thermomechanical response of changing the via spacing. It is found that the DSC model predictions provide satisfactory comparison with a previous analysis by others, and with observed laboratory behavior.