| Soldering is extensively used to assemble electronic components to printed circuit boards or chips to substrates in Microsystems. Solder joints serve as mechanical, thermal, and electrical interconnections, therefore, solder joint integrity is a key reliability concern. Predicting the reliability of solder joints is a complex problem due to its operation at high homologous temperatures coupled with the complex package design, stress, solder microstructure, and fatigue mechanisms in solder joints.; In the research presented here, different techniques in fatigue life prediction of solder joints as well as experimental procedures and microstructural analysis, are developed. The environmental conditions include an accelerated temperature cycling test and a more recent power cycling test, recently developed and believed as being more representative of the filed use conditions.; An examination of the local deformation mechanisms in the solder joints coupled with finite element simulations to elucidate local fatigue/creep driving forces can provide a more comprehensive understanding of the cyclic degradation processes. A thorough examination of fracture surfaces of solder joints extensively reported in this thesis reveals failure mechanisms induced by environmental conditions. The understanding of the relationship between the microstructural deformation mechanisms and the applied thermal stresses engenders failure models and standards that are in agreement with physical damage processes.; At the end, to alleviate the computational expense that has been a main drawback of non-empirical physics-based approaches, a hybrid fracture-damage approach is proposed. The selected cohesive zone model of Smith-Ferrante form was found to evolve in a manner similar to the continuum damage mechanics theory. This damage definition is therefore used to make decisions on crack progression. The fatigue life estimation and the predicted crack trajectories are in excellent agreement with experimental data and show promise in analyzing fatigue crack growth problems. More importantly, the calculated rate of damage change from the model shows excellent correlation with the microstructural change on the fracture surface of solder joint. |
