| Pb/Sn solder joints are extensively used as surface mount technology (SMT) packaging interconnects. Thermal cycling of semiconductor devices induces thermal fatigue in solder joints. On the other hand, when such devices are used in automotive and military applications, they are subjected to severe vibrations. There is very little research results reported in the literature on the subject of concurrent dynamic/thermal analysis of solder joints. The primary objective of this research is to develop a constitutive model for Pb/Sn solder to study reliability of power electronics and SMT interconnects under dynamic, thermal and concurrent dynamic and thermal loadings.; Solder is a highly nonlinear material and exhibits time dependent viscous behavior. So a viscoplasticity based constitutive model is developed. A thermo dynamic damage theory is implemented in the model along with effect of microstructure to analyze the distribution and progress of damage in the solder joints and the number of cycles to failure. A nonlinear viscoplastic finite element algorithm is then developed which implements the damage mechanics based constitutive model.; In order to verify the constitutive model, a number of case studies are considered and numerical predictions are compared against test data. Several boundary value problems and parametric studies have been solved under thermal, dynamic and concurrent conditions to determine the stress distribution, damage and to assess the fatigue life. The objective of the parametric study is to understand the mechanical behavior of solder joints under different load and boundary conditions.; The important scientific contribution of this dissertation is development of a new constitutive model for Pb/Sn solder taking into account the grain size and damage mechanics. Pb/Sn solder alloys are thermodynamically unstable materials and as they are aged or deformed, they become thermodynamically stable. Their thermomechanical behavior is dependent on microstructure, which in turn depends on solidification or cooling rate. The constitutive model has been developed to characterize this behavior. A new yield surface has been proposed in this dissertation. Coupled dynamic-thermal viscoplastic-damage analysis of eutectic solder alloys is also a major contribution of this dissertation. |
